RAID- Redudat array of Independent Disk (Orginally Redudant Array of Inexpensive Disk)
RAID is a data storage technology that combines multiple disk drive components into a logical unit for the purposes of data redundancy and performance improvement. Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the specific level of redundancy and performance required.
1- RAID is used as a term for computer data Storage schemed that can devide and
replicate data among multiple physical drive.
2- The physical drives are said to be in a RAID which is accessed by the os
as one single drive.
3- The different schemes are named by the word RAID followed by a number (e.q.
RAID-0 RAID-1)
4- Each scheme provides a different balance between two key goals:
a. Increase data reliability and
b. Increase input/output performance
RHEL Supports-
1- RAID 0 Striping
2- RAID 1 Mirroring
3- RAID 4 Disk striping with Praity and one disk reserve for parity
4- RAID 5 Disk Striping with Single Distribuited Parity
5- RAID 6 Disk Striping with Dual distributed parity
6- RAID 10 Combination of RAID 0 and RAID 1
Command Used- mdadm
The name is derived from the md (multiple device) device nodes is administers or manages
mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sda1 /dev/sdb1
Note- If we want to Change RAID level we can use level switch with following..
--level=0
--level=1
--level=4
--level=5
--level=6
--level=10
RAID 0 (Striping )
1- RAID 0 requies at least two RAID partitions
2- Distributes data across multiple storage device
3- Level 0 RAIDs offer increased performance over standard partition ,and
4- can be used to pool the storage of multiple device into one large virtual device
5- Level 0 RAIDs offer no redudancy and that the failure of one device in the
array destroys the entire array.
Configure RAID 0-
Step-1. Create 2 Partition
Create a Partition Read...
There are use 2 hdd partition like..
1- /dev/sda1
2- /dev/sdb1
Step-2 We can create RAID 0 array on the'mdadm' command
# mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sda1 /dev/sdb1
Now mdadm: array /dev/md0 started..
Step-3 Check Detais..
# mdadm --detail /dev/md0 (/dev/md0 is a raid device name)
Step-4 How to use raid 0
1- Formate /dev/md0
# mkfs.ext4 /dev/md0
2- Mount /dev/md0
# mkdir /RAID0
# mount /dev/md0 /RAID0
# mount
How to Remove RAID 0
Step- 1 Umount /dev/md0
# umount /RAID0
# mount
Step- 2 Distroy RAID 0
# mdadm --stop /dev/md0 (/dev/md0 is a device name)
Step-3 Now Again check Details
# mdadm --detail /dev/ md0
/dev/md0: no such file or directory
_________________________________________________________
RAID 1 (Mirroring)
1- RAID Level 1 provides redudancy by writing identical data to each member disk of the array, leaving a "mirrored" copy on each disk
2- Popular due to its simplicity and high level of data avalibility .
3- Operates with two or more disks.
4- Provide very good data reliability and improve performance for read-intensive application but at a relatively high cost
5- The storage capacity of the level 1 array is equal to the capacity of the smallest mirrored hard disk in a Hardware RAID or the smallest mirrored partition in a software RAID.
6- Level 1 redudancy is the highest possible among all RAID types, with the array being able to operate with only a single disk present.
Configure RAID 1-
Step-1. Create Primary partition on each member disk of the array using fdisk utility.
Create a Partition Read...
There are use 2 hdd partition ..
1- /dev/sda1
2- /dev/sdb1
Step-2 We can create RAID 1 array on the'mdadm' command
# mdadm --create /dev/md1 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb1
Now mdadm: array /dev/md1 started..
Step-3 Check Detais..
# mdadm --detail /dev/md1 (/dev/md1 is a raid device name)
Step-4 How to use raid 1
1- Formate /dev/md1
# mkfs.ext4 /dev/md1
2- Mount /dev/md1 # mkdir /RAID1
# mount /dev/md1 /RAID1
# mount
How to Remove RAID 1
Step- 1 Umount /dev/md1
# umount /RAID1
# mount
Step- 2 Distroy RAID 1
# mdadm --stop /dev/md1 (/dev/md1 is a device name)
Step-3 Now Again check Details
# mdadm --detail /dev/ md0
/dev/md1: no such file or directory
_________________________________________________________
RAID 5 (Disk Striping with Single Distribuited Parity)
1- Minimum 3 HDD or 3 Partition
2- Provide good performance as block are striped
3- Provide good redudancy , distributed parity
4- Best cost effective option providing both performance and redudancy.
5- RAID level 5 is equal to the capacity of the member partitions, mins the size
of the partition if they are equal size.
6- RAID 5 read write speeds are good.
7- RAID 5 alwayes use -1 hdd.(e.q.3 hdd space- 10GB+10GB+10GB= 20GB Space).
8- Can handle 1 disk failure.
Configure RAID 5-
Step-1. Create Primary partition on each member disk of the array using fdisk utility.
Create a Partition Read...
There are use 3 partition like ..
1- /dev/sda1
2- /dev/sdb1
3- /dev/sdc1
Step-2 We can create RAID 5 array on the'mdadm' command
# mdadm --create /dev/md5 --level=5 --raid-devices=3 /dev/sda1 /dev/sdb1 /dev/sdc1
Now mdadm: array /dev/md5 started..
Step-3 Check Detais..
# mdadm --detail /dev/md5 (/dev/md5 is a raid device name)
Step-4 How to use raid 5
1- Formate /dev/md5
# mkfs.ext4 /dev/md5
2- Mount /dev/md5
# mkdir /RAID5
# mount /dev/md5 /RAID5
# mount
How to Remove RAID 5
Step- 1 Umount /dev/md5
# umount /RAID5
# mount
Step- 2 Distroy RAID 5
# mdadm --stop /dev/md5 (/dev/md5 is a device name)
Step-3 Now Again check Details
# mdadm --detail /dev/ md5
/dev/md5: no such file or directory
_________________________________________________________
RAID 6 (Disk Striping with Dual distributed parity)
1- Min HDD 4
2- This create two parity blocks for each data block.
3- Can handle 2 disk failure
4- This RAID configuration is complex to implement in a RAID controller, as it has to calculate two parity data for each data block.
5- RAID 6 alwayes use -2 hdd.(e.q.4 hdd space-> 10GB+10GB+10GB+10GB= 20GB Space).
Configure RAID 6-
Step-1. Create Primary partition on each member disk of the array using fdisk utility.
Create a Partition Read...
There are use 4 hdd partition like.
1- /dev/sda1
2- /dev/sdb1
3- /dev/sdc1
4- /dev/sdd1
Step-2 We can create RAID 6 array on the'mdadm' command
# mdadm --create /dev/md6 --level=6 --raid-devices=4 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1
Now mdadm: array /dev/md6 started..
Step-3 Check Detais or Display..
# mdadm --detail /dev/md6 (/dev/md6 is a raid device name)
Step-4 How to use raid 6
1- Formate /dev/md6
# mkfs.ext4 /dev/md6
2- Mount /dev/md6
# mkdir /RAID6
# mount /dev/md6 /RAID6
# mount
How to Remove RAID 6
Step- 1 Umount /dev/md6
# umount /RAID6
# mount
Step- 2 Distroy RAID 6
# mdadm --stop /dev/md6 (/dev/md6 is a device name)
Step-3 Now Again check Details
# mdadm --detail /dev/ md6
/dev/md6: no such file or directory
_________________________________________________________
How to extend disk in RAID-
Suppose I want to extand hdd in raid level 6 or other RAID level..
hdd- /dev/sde1
# mdadm --add /dev/md6 /dev/sde1
Note: '/dev/md6'- RAID Level and '/dev/sde1' your new hdd.
Sucessefully add this hdd.
Then..
How to grow RAID array..
# mdadm --grow /dev/md6 --raid-device=5
# mdadm --detail /dev/md6
_________________________________________________________
RAID 10 (Combination of RAID 0 and RAID 1)
1- Minimum 4 disks.
2- This is also called as “stripe of mirrors”
3- Excellent redundancy ( as blocks are mirrored )
4- Excellent performance ( as blocks are striped )
5- If you can afford the dollar, this is the BEST option for any mission critical applications (especially databases).
Configure RAID 10-
Step-1. Create Primary partition on each member disk of the array using fdisk utility.
Create a Partition Read...
There are use 4 hdd partition like.
1- /dev/sda1
2- /dev/sdb1
3- /dev/sdc1
4- /dev/sdd1
Step-2 We can create RAID 10 array on the'mdadm' command
# mdadm --create /dev/md10 --level=10 --raid-devices=4 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1
Now mdadm: array /dev/md10 started..
Step-3 Check Detais or Display..
# mdadm --detail /dev/md10 (/dev/md6 is a raid device name)
Step-4 How to use raid 10
1- Formate /dev/md10
# mkfs.ext4 /dev/md10
2- Mount /dev/md10
# mkdir /RAID10
# mount /dev/md10 /RAID10
# mount
How to Remove RAID 10
Step- 1 Umount /dev/md10
# umount /RAID10
# mount
Step- 2 Distroy RAID 10
# mdadm --stop /dev/md10 (/dev/md10 is a device name)
Step-3 Now Again check Details
# mdadm --detail /dev/ md10
/dev/md10: no such file or directory
So Enjoy,...
RAID Interview Question & Answer-
Yes, we can create Software RAID during Linux Installation by “Disk Druid”
RAID is a data storage technology that combines multiple disk drive components into a logical unit for the purposes of data redundancy and performance improvement. Data is distributed across the drives in one of several ways, referred to as RAID levels, depending on the specific level of redundancy and performance required.
1- RAID is used as a term for computer data Storage schemed that can devide and
replicate data among multiple physical drive.
2- The physical drives are said to be in a RAID which is accessed by the os
as one single drive.
3- The different schemes are named by the word RAID followed by a number (e.q.
RAID-0 RAID-1)
4- Each scheme provides a different balance between two key goals:
a. Increase data reliability and
b. Increase input/output performance
RHEL Supports-
1- RAID 0 Striping
2- RAID 1 Mirroring
3- RAID 4 Disk striping with Praity and one disk reserve for parity
4- RAID 5 Disk Striping with Single Distribuited Parity
5- RAID 6 Disk Striping with Dual distributed parity
6- RAID 10 Combination of RAID 0 and RAID 1
Command Used- mdadm
The name is derived from the md (multiple device) device nodes is administers or manages
mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sda1 /dev/sdb1
Note- If we want to Change RAID level we can use level switch with following..
--level=0
--level=1
--level=4
--level=5
--level=6
--level=10
RAID 0 (Striping )
1- RAID 0 requies at least two RAID partitions
2- Distributes data across multiple storage device
3- Level 0 RAIDs offer increased performance over standard partition ,and
4- can be used to pool the storage of multiple device into one large virtual device
5- Level 0 RAIDs offer no redudancy and that the failure of one device in the
array destroys the entire array.
Configure RAID 0-
Step-1. Create 2 Partition
Create a Partition Read...
There are use 2 hdd partition like..
1- /dev/sda1
2- /dev/sdb1
Step-2 We can create RAID 0 array on the'mdadm' command
# mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sda1 /dev/sdb1
Now mdadm: array /dev/md0 started..
Step-3 Check Detais..
# mdadm --detail /dev/md0 (/dev/md0 is a raid device name)
Step-4 How to use raid 0
1- Formate /dev/md0
# mkfs.ext4 /dev/md0
2- Mount /dev/md0
# mkdir /RAID0
# mount /dev/md0 /RAID0
# mount
How to Remove RAID 0
Step- 1 Umount /dev/md0
# umount /RAID0
# mount
Step- 2 Distroy RAID 0
# mdadm --stop /dev/md0 (/dev/md0 is a device name)
Step-3 Now Again check Details
# mdadm --detail /dev/ md0
/dev/md0: no such file or directory
_________________________________________________________
RAID 1 (Mirroring)
1- RAID Level 1 provides redudancy by writing identical data to each member disk of the array, leaving a "mirrored" copy on each disk
2- Popular due to its simplicity and high level of data avalibility .
3- Operates with two or more disks.
4- Provide very good data reliability and improve performance for read-intensive application but at a relatively high cost
5- The storage capacity of the level 1 array is equal to the capacity of the smallest mirrored hard disk in a Hardware RAID or the smallest mirrored partition in a software RAID.
6- Level 1 redudancy is the highest possible among all RAID types, with the array being able to operate with only a single disk present.
Configure RAID 1-
Step-1. Create Primary partition on each member disk of the array using fdisk utility.
Create a Partition Read...
There are use 2 hdd partition ..
1- /dev/sda1
2- /dev/sdb1
Step-2 We can create RAID 1 array on the'mdadm' command
# mdadm --create /dev/md1 --level=1 --raid-devices=2 /dev/sda1 /dev/sdb1
Now mdadm: array /dev/md1 started..
Step-3 Check Detais..
# mdadm --detail /dev/md1 (/dev/md1 is a raid device name)
Step-4 How to use raid 1
1- Formate /dev/md1
# mkfs.ext4 /dev/md1
2- Mount /dev/md1 # mkdir /RAID1
# mount /dev/md1 /RAID1
# mount
How to Remove RAID 1
Step- 1 Umount /dev/md1
# umount /RAID1
# mount
Step- 2 Distroy RAID 1
# mdadm --stop /dev/md1 (/dev/md1 is a device name)
Step-3 Now Again check Details
# mdadm --detail /dev/ md0
/dev/md1: no such file or directory
_________________________________________________________
RAID 5 (Disk Striping with Single Distribuited Parity)
1- Minimum 3 HDD or 3 Partition
2- Provide good performance as block are striped
3- Provide good redudancy , distributed parity
4- Best cost effective option providing both performance and redudancy.
5- RAID level 5 is equal to the capacity of the member partitions, mins the size
of the partition if they are equal size.
6- RAID 5 read write speeds are good.
7- RAID 5 alwayes use -1 hdd.(e.q.3 hdd space- 10GB+10GB+10GB= 20GB Space).
8- Can handle 1 disk failure.
Configure RAID 5-
Step-1. Create Primary partition on each member disk of the array using fdisk utility.
Create a Partition Read...
There are use 3 partition like ..
1- /dev/sda1
2- /dev/sdb1
3- /dev/sdc1
Step-2 We can create RAID 5 array on the'mdadm' command
# mdadm --create /dev/md5 --level=5 --raid-devices=3 /dev/sda1 /dev/sdb1 /dev/sdc1
Now mdadm: array /dev/md5 started..
Step-3 Check Detais..
# mdadm --detail /dev/md5 (/dev/md5 is a raid device name)
Step-4 How to use raid 5
1- Formate /dev/md5
# mkfs.ext4 /dev/md5
2- Mount /dev/md5
# mkdir /RAID5
# mount /dev/md5 /RAID5
# mount
How to Remove RAID 5
Step- 1 Umount /dev/md5
# umount /RAID5
# mount
Step- 2 Distroy RAID 5
# mdadm --stop /dev/md5 (/dev/md5 is a device name)
Step-3 Now Again check Details
# mdadm --detail /dev/ md5
/dev/md5: no such file or directory
_________________________________________________________
RAID 6 (Disk Striping with Dual distributed parity)
1- Min HDD 4
2- This create two parity blocks for each data block.
3- Can handle 2 disk failure
4- This RAID configuration is complex to implement in a RAID controller, as it has to calculate two parity data for each data block.
5- RAID 6 alwayes use -2 hdd.(e.q.4 hdd space-> 10GB+10GB+10GB+10GB= 20GB Space).
Configure RAID 6-
Step-1. Create Primary partition on each member disk of the array using fdisk utility.
Create a Partition Read...
There are use 4 hdd partition like.
1- /dev/sda1
2- /dev/sdb1
3- /dev/sdc1
4- /dev/sdd1
Step-2 We can create RAID 6 array on the'mdadm' command
# mdadm --create /dev/md6 --level=6 --raid-devices=4 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1
Now mdadm: array /dev/md6 started..
Step-3 Check Detais or Display..
# mdadm --detail /dev/md6 (/dev/md6 is a raid device name)
Step-4 How to use raid 6
1- Formate /dev/md6
# mkfs.ext4 /dev/md6
2- Mount /dev/md6
# mkdir /RAID6
# mount /dev/md6 /RAID6
# mount
How to Remove RAID 6
Step- 1 Umount /dev/md6
# umount /RAID6
# mount
Step- 2 Distroy RAID 6
# mdadm --stop /dev/md6 (/dev/md6 is a device name)
Step-3 Now Again check Details
# mdadm --detail /dev/ md6
/dev/md6: no such file or directory
_________________________________________________________
How to extend disk in RAID-
Suppose I want to extand hdd in raid level 6 or other RAID level..
hdd- /dev/sde1
# mdadm --add /dev/md6 /dev/sde1
Note: '/dev/md6'- RAID Level and '/dev/sde1' your new hdd.
Sucessefully add this hdd.
Then..
How to grow RAID array..
# mdadm --grow /dev/md6 --raid-device=5
# mdadm --detail /dev/md6
_________________________________________________________
RAID 10 (Combination of RAID 0 and RAID 1)
1- Minimum 4 disks.
2- This is also called as “stripe of mirrors”
3- Excellent redundancy ( as blocks are mirrored )
4- Excellent performance ( as blocks are striped )
5- If you can afford the dollar, this is the BEST option for any mission critical applications (especially databases).
Configure RAID 10-
Step-1. Create Primary partition on each member disk of the array using fdisk utility.
Create a Partition Read...
There are use 4 hdd partition like.
1- /dev/sda1
2- /dev/sdb1
3- /dev/sdc1
4- /dev/sdd1
Step-2 We can create RAID 10 array on the'mdadm' command
# mdadm --create /dev/md10 --level=10 --raid-devices=4 /dev/sda1 /dev/sdb1 /dev/sdc1 /dev/sdd1
Now mdadm: array /dev/md10 started..
Step-3 Check Detais or Display..
# mdadm --detail /dev/md10 (/dev/md6 is a raid device name)
Step-4 How to use raid 10
1- Formate /dev/md10
# mkfs.ext4 /dev/md10
2- Mount /dev/md10
# mkdir /RAID10
# mount /dev/md10 /RAID10
# mount
How to Remove RAID 10
Step- 1 Umount /dev/md10
# umount /RAID10
# mount
Step- 2 Distroy RAID 10
# mdadm --stop /dev/md10 (/dev/md10 is a device name)
Step-3 Now Again check Details
# mdadm --detail /dev/ md10
/dev/md10: no such file or directory
So Enjoy,...
_____________________________________________________________________________________________
RAID Interview Question & Answer-
1-what
is redundancy ?
Writing
to two or more disks at the same time. Having the same data stored on
separate disks enables the data to be recovered in the event of a
disk failure without resorting to expensive data recovery techniques
2-what
is disk mirroring ?
a
simple computer, data is stored on a single hard disk. Disk
mirroring stores the same data to two separate disks at once. If
one disk fails, all the information is still available on the other
disk.
3-what
is disk block ?
A
block is a set of bits or bytes that forms an identifiable unit of
data. The term is used in database management, word processing, and
network communication
4-what
is disk striping ?
In
computers that use multiple hard disk systems, disk striping is the
process of dividing a body of data into blocks and spreading the data
blocks across several partitions
on several hard
disks.
Each stripe is the size of the smallest partition. For example, if
three partitions are selected with one partition equaling
150megabytes, another 100MB, and the third 50MB, each stripe will be
50 MB in size. It is wise to create the partitions equal in size to
prevent wasting disk space. Each stripe created is part of the stripe
set. Disk striping is used with redundant array of independent disks
(RAID). RAID is a storage system that uses multiple disks to store
and distribute data. Up to 32 hard disks can be used with disk
striping.
There
are two types of disk striping: single user and multi-user. Single
user disk striping allows multiple hard disks to simultaneously
service multiple I/O requests
from a single workstation. Multi-user disk striping allows multiple
I/O requests from several workstations to be sent to multiple hard
disks. This means that while one hard disk is servicing a request
from a workstation, another hard disk is handling a separate request
from a different workstation.
5-what
is parity in raid ?
Parity
computations are used in RAID drive arrays for fault tolerance by
calculating the data in two drives and storing the results on a
third. The parity is computed by XOR'ing a bit from drive 1 with a
bit from drive 2 and storing the result on drive 3 (to learn about
XOR, see OR).
After a failed drive is replaced, the RAID controller rebuilds the
lost data from the other two drives. RAID systems often have a "hot"
spare drive ready and waiting to replace a drive that fails. See
6-what
is fault tolerance ?
Fault
tolerance is the ability of a system to continue working even when a
fault exists. In the case of RAID, which stands for Redundant Array
of Inexpensive Discs, fault tolerance is provided by
having
data recorded on more than one drive, and also by having more than
one power supply. Note that RAID 0 is not fault telerant because it
is simply stripes the data to increase size and bandwidth,
but
provides no redundancy. RAID 1 and RAID 5 are fault tolerant, to
various levels.
7-what
is disk array ?
A disk
array is a hardware element that contains a large group of hard disk
drives (HDDs). It may contain several disk
drive trays and has an architecture which
improves speed and increases data protection. The system is run via a
storage controller, which coordinates activity within the unit. Disk
arrays form the backbone of modern storage
networking environments. A storage area
network (SAN)
contains one or more disk arrays that function as the repository for
the data which is moved in and out of the SAN.
8-what
is disk SAN ?
A
Storage area network, or SAN, is a high-speed network of storage
devices that also connects those storage devices with servers. It
provides block-level storage that can be accessed by the applications
running on any networked servers. SAN storage devices can include
tape libraries, and, more commonly, disk-based devices,
like RAID hardware.
9-what
is disk RAID ?
Originally,
the term RAID stood for "redundant array of inexpensivedisks,"
but now it usually refers to a "redundant array
ofindependent disks."
While older storage devices used only one disk drive to store data,
RAID storage uses multiple disks in order to provide fault tolerance,
to improve overall performance, and to increase storage capacity in a
system.
With
RAID technology, data can be mirrored on one or more other disks in
the same array, so that if one disk fails, the data is preserved.
Thanks to a technique known as "striping," RAID also offers
the option of reading or writing to more than one disk at the same
time in order to improve performance. In this arrangement, sequential
data is broken into segments which are sent to the various disks in
the array, speeding up throughput. Also, because a RAID array uses
multiple disks that appear to be a single device, it can often
provide more storage capacity than a single disk.
10-What
is the difference between hardware RAID and Software RAID?
The
hardware-based RAID is independent from the host. A Hardware RAID
device connects to the SCSI controller and presents the RAID arrays
as a single SCSI drive. An external RAID system moves all RAID
handling "intelligence" into a controller located in the
external disk subsystem. The whole subsystem is connected to the host
via a normal SCSI controller and appears to the host as a single
disk.
Software
RAID is implemented under OS Kernel level. The Linux kernel contains
an MD driver that allows the RAID solution to be completely hardware
independent. The performance of a software-based array depends on the
server CPU performance and load.
11-What
are the commonly used RAID types?
RAID 0
RAID 1
RAID 5
RAID 0
RAID 1
RAID 5
12-Explain
RAID 0?
RAID level 0 works on “striping” technique. In RAID 0 the array is broken down into strips and data is written into strips. RAID 0 allows high I/O performance but provides no redundancy. RAID 0 Array Size is equal to sum of disks in array. If one drive fails then all data in the array is lost.
RAID level 0 works on “striping” technique. In RAID 0 the array is broken down into strips and data is written into strips. RAID 0 allows high I/O performance but provides no redundancy. RAID 0 Array Size is equal to sum of disks in array. If one drive fails then all data in the array is lost.
13-Explain
RAID 1?
RAID Level 1 is based on Mirroring technique. Level 1 provides redundancy by writing identical data to each member disk of the array. The storage capacity of the level 1 array is equal to the capacity of one of the mirrored hard disks in a Hardware RAID or one of the mirrored partitions in a Software RAID. RAID 1 provides redundancy means good protection against disk failure. In RAID 1 write speed is slow but read speed is good.
RAID Level 1 is based on Mirroring technique. Level 1 provides redundancy by writing identical data to each member disk of the array. The storage capacity of the level 1 array is equal to the capacity of one of the mirrored hard disks in a Hardware RAID or one of the mirrored partitions in a Software RAID. RAID 1 provides redundancy means good protection against disk failure. In RAID 1 write speed is slow but read speed is good.
14-Explain
RAID 5?
RAID Level 5 is based on rotating parity with striping technique. RAID-5 stores parity information but not redundant data (but parity information can be used to reconstruct data). The storage capacity of Software RAID level 5 is equal to the capacity of the member partitions, minus the size of one of the partitions if they are of equal size. The performance of RAID 5 is based on parity calculation process but with modern CPUs that usually is not a very big problem. In RAID 5 read and write speeds are good.
RAID Level 5 is based on rotating parity with striping technique. RAID-5 stores parity information but not redundant data (but parity information can be used to reconstruct data). The storage capacity of Software RAID level 5 is equal to the capacity of the member partitions, minus the size of one of the partitions if they are of equal size. The performance of RAID 5 is based on parity calculation process but with modern CPUs that usually is not a very big problem. In RAID 5 read and write speeds are good.
15-Which
kernel module is required for Software RAID?
“md” module
“md” module
16-which
utility or command is used for creating software RAID’s for
RHEL5?
mdadm
mdadm
17-Can
we create software RAID during Linux installation?
Yes, we can create Software RAID during Linux Installation by “Disk Druid”
18-What
is the role of chunk size for software RAID?
Chunk size is very important parameter on which RAID performance based.
We know stripes go across disk drives. But how big are the pieces of the stripe on each disk? The pieces a stripe is broken into are called chunks.To get good performance you must have a reasonable chunk size.
Chunk size is very important parameter on which RAID performance based.
We know stripes go across disk drives. But how big are the pieces of the stripe on each disk? The pieces a stripe is broken into are called chunks.To get good performance you must have a reasonable chunk size.
For
big I/Os we required small chunks and for small I/Os we required big
chunks.
19-What
is SWAP Space?
Swap space in Linux is used when the amount of physical memory (RAM) is full. If the system needs more memory resources and the RAM is full, inactive pages in memory are moved to the swap space. While swap space can help machines with a small amount of RAM, it should not be considered a replacement for more RAM. Swap space is located on hard drives, which have a slower access time than physical memory.
Swap space in Linux is used when the amount of physical memory (RAM) is full. If the system needs more memory resources and the RAM is full, inactive pages in memory are moved to the swap space. While swap space can help machines with a small amount of RAM, it should not be considered a replacement for more RAM. Swap space is located on hard drives, which have a slower access time than physical memory.
20-What
are the steps to create SWAP files or Partition?
- Create swap partition or file
- Write special signature using “mkswap”
- Activate swap space by “swapon –a” command
- Add swap entry into /etc/fstab file
- Create swap partition or file
- Write special signature using “mkswap”
- Activate swap space by “swapon –a” command
- Add swap entry into /etc/fstab file
21-How
you will create swap file of size 4 GB and explain swap file entry in
/etc/fstab file?
Use “dd” command to create swap file.
Use “dd” command to create swap file.
dd
if=/dev/zero of=/SWAPFILE bs=1024 count=4
mkswap
/SWAPFILE
swapon
–a
Entry
into /etc/fstab file.
/SWAPFILE
swap swap defaults 0
0
22-What
are the advantages and disadvantage of RAID?
Advantages:
- RAID allows form of backup of the data in the storage array in the event of a failure
- In event failure, if one of the drives fails then either drive swapped out for a new drive without turning the systems off also known as hot swappable
- OR the redundant drive could be used
- Ensures data reliability, increase in Input Output performance and shadowing/Mirroring at a lower cost
- Increase the parity check and regularly checks for any possible system crash
- Provides Disk Stripping to write data to disk, which improves performance by the interleaving of the bytes or the group of bytes.
- Disk Stripping make multiple smaller disks look like one large disk
- Reading and Writing of data done at simultaneously.
- Mirroring for 100% duplication of data on two drives.
- Mirroring offers parity check to ensure data from crashed system be matched with the data stored on to the other disk.
Disadvantages:
- RAID doesn’t make data recovery any easier.
- RAID cannot completely protect your data.
- RAID doesn’t always result in improved system performance.
- Costly, must purchase and maintain RAID the controllers and dedicated hard drives
- Have to be maintained by highly paid consultants.
- They may slower the system performance if not used properly
- RAID is not data protection, but to increase access speed
- If your data is not being backed up offsite, security is still concerned
- more work to do like installing drivers, updating firmware and running consistency checks
23-Whats
the difference between RAID0 & RAID1 ?
RAID 0 |
RAID 1 |
|
Where data loss is
unaceptable e.g. Data archival
|
24-How
many minimum disk drives are needed for R0,R1,R5,R10,R01?
R0:
Minimum 1
R1:
Minimum 2
R5:
Minimum 3
R10:
Minimum 4
R01:
Minimum 4
25-Whats
the difference between RAID3 & RAID5 ?
RAID 3
and RAID 4: Striped Set (3 disk minimum) with Dedicated Parity, the
parity bits represent a memory location each, they have a value of 0
or 1, whether the given memory location is empty or full, thus
enhancing the speed of read and write. : Provides improved
performance and fault tolerance similar to RAID 5, but with a
dedicated parity disk rather than rotated parity stripes. The single
disk is a bottle-neck for writing since every write requires updating
the parity data. One minor benefit is the dedicated parity disk
allows the parity drive to fail and operation will continue without
parity or performance penalty.
RAID 5
does not have a dedicated parity drive but the parity is rotated
across all the drives hence the parity is distributed.
RAID
5: Striped Set (3 disk minimum) with Distributed Parity: Distributed
parity requires all but one drive to be present to operate; drive
failure requires replacement, but the array is not destroyed by a
single drive failure. Upon drive failure, any subsequent reads can be
calculated from the distributed parity such that the drive failure is
masked from the end user. The array will have data loss in the event
of a second drive failure and is vulnerable until the data that was
on the failed drive is rebuilt onto a replacement drive.
26-Whats
the difference between RAID01 & RAID10 ?
RAID
0+1: Striped Set + Mirrored Set (4 disk minimum; Even number of
disks) provides fault tolerance and improved performance but
increases complexity. Array continues to operate with one failed
drive. The key difference from RAID 1+0 is that RAID 0+1 creates a
second striped set to mirror a primary striped set, and as a result
can only sustain a maximum of a single disk loss, whereas 1+0 can
sustain multiple drive losses as long as no two drive loss comprise a
single pair.
RAID
1+0: Mirrored Set + Striped Set (4 disk minimum; Even number of
disks) provides fault tolerance and improved performance but
increases complexity. Array continues to operate with one or more
failed drives. The key difference from RAID 0+1 is that RAID 1+0
creates a striped set from a series of mirrored drives.
27-How
RAID 5 works and how parity is calculated ?
The
parity calculation is typically performed using a logical operation
called "exclusive OR" or "XOR". As you may know,
the "OR" logical operator is "true" (1) if either
of its operands is true, and false (0) if neither is true. The
exclusive OR operator is "true" if and only if one of its
operands is true; it differs from "OR" in that if both
operands are true, "XOR" is false.
28-Other
than RAID feature what are the other features in Software
Management
Functionalities?
Hotspare
Raid
level migration (RLM)
SNMP
interaction/management
29-What
is initialization ?
Intialization
is the process of preparing a drive for storage use. It erases all
data on the drive & makes way for new file system creation.
30-What
is Check consistency ?
Consistency
check or CC verifies correctness of data in logical drives. This is a
feature of some of the RAID hardware controller cards.
31-What
is background initialization?
This
is a Consistency check process forced when a new logical drive is
created. This is an automatic operation that starts 5 minutes after
the new logical drive is created.
32-What
is a RAID array ?
RAID
array is a group of disks which are configured with RAID. That means
they are in a redundant setup to tolerate any disk failures.
33-Whats
the difference between a JBOD & a RAID array ?
Just A
Bunch Of Disks (JBOD) - hard disks that aren't configured in a RAID
configuration. They are just disks piled or connected in one single
enclosure.
RAID
is having the advantage of bearing a disk failure & still give
data availability.
34-When
JBOD is preferred over RAID array ?
When
there is no need for redundancy & when it is ok if there is some
hard disk failure or data unavilability in such scenarios JBOD is
prefered over RAID because JBOD is inexpensive storage solution. It
is also easy to setup & start using compared to RAID.
35-What
is a hot spare ?
Hot
spare is an extra,unused disk drive that is part of the disk
subsystem. It is usually in standby mode ready for service if a drive
fails. Whenever there is a drive failure this hotspare kicksin &
takes over that failed drive's role.
36-What
is a Logical drive or Virtual drive ?
The
partitioning or division of a large hard drive into smaller units. A
single, large Physical Drive can be partitioned into two or more
smaller Logical Drives.
37-What
is rebuilding of array ?
Whenever
there is a disk failure in the RAID array the array goes to
DOWNGRADED STATE. SO when we plug out the failed drive & insert a
new functioning drive the RAID configured array starts regenerating
the data to the newer drive. This process is called rebuilding.
38-What
you do when a drive in an array fails, how you bring it back to
optimal online mode ?
We
swap out failed drive & plugin new functioning drive & wait
for the rebuilding process to complete. We make sure rebuild process
happens without any error. Once that completes array is back to
optimal online state.
39-What
are the different states an array can be in and explain each state?
Online
Downgraded
Offline
Rebuilding
40-Explain
Online,Offline,Degraded states of an array ?
Online
- when all drives are working fine
Downgraded
- Whenever there is a drive failure but still the array is
functioning fine
Offline
- Array or whole data storage is down
Rebuilding
- Storage access is there but since a new drive has been inserted in
place of a failed drive data is being written to new drive which
might slow down the performance of the whole RAID array.
41-What
is the difference between a global hotspare & a dedicated
hotspare ?
Global
hotpsare is available for the any array in the whole enclosure
or Storage subsystem.
If
there is an enclosure having 10 drives & we have 3 drives in
RAID5(1st array) , 3 more drives in second RAID5(2nd array) & 2
more drives in RAID 1 config.We can specify in RAID config utility
whether a Dedicated hotspare is assigned for 1st RAID5 array. If
there is a drive failure in 2nd or 3rd array this dedicated hotspare
will not be involved there. But if the array for which this is
dedicated has any drive failure this dedicated hotspare takes over .
42-How
RAID is configured through BIOS ?
If we
have a Hardware RAID controller card it gives an option while machine
booting to enter into RAID BIOS utility. Here we have options which
give us options to create RAID using a semi-GUI(DOS based GUI)
interface.
43-HoW
RAID is configured in OS level?
Once
we install device drivers & also RAID config or management
utility using that we can configure RAID in OS level.
44-What
is the difference between a software RAID & hardware RAID ?
In
order for RAID to function, there needs to be software either through
the operating system or via dedicated hardware to properly handle the
flow of data from the computer system to the drive array. This is
particularly important when it comes to RAID 5 due to the large
amount of computing required to generate the parity calculations.
In the
case of software implementations, CPU cycles are taken away from the
general computing environment to perform the necessary tasks for the
RAID interface. Software implementations are very low cost monetarily
because all that is necessary to implement one is the hard drives.
The problem with software RAID implementations is the performance
drop of the system. In general, this performance hit can be anywhere
from 5% or even greater depending upon the processor, memory, drives
used and the level of RAID implemented. Most people do not use
software RAID anymore due to the decreasing costs of hardware RAID
controllers over the years.
Hardware
RAID has the advantage of dedicated circuitry to handle all the RAID
drive array calculations outside of the processor. This provides
excellent performance for the storage array. The drawbacks to
hardware RAID have been the costs. In the case of RAID 0/1
controllers, those costs have become so low that many chipset and
motherboard manufacturers are including these capabilities on the
motherboards. The real costs rest with RAID 5 hardware that require
more circuitry for added computing ability.
45-Which
is best RAID level for performance and which is best for redundancy?
RAID 0
for performance
RAID 5
or RAID 6 better for redundancy(availibility)
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