Part 1: Introduction to RAID, Concepts of RAID and RAID Levels
Part 2: How to setup RAID0 (Stripe) in Linux
Part 3: How to setup RAID1 (Mirror) in Linux
Part 4: How to setup RAID5 (Striping with Distributed Parity) in Linux
Part 5: How to setup RAID6 (Striping with Double Distributed Parity) in Linux
Part 6: Setting Up RAID 10 or 1+0 (Nested) in Linux
Part 7: Growing an Existing RAID Array and Removing Failed Disks in Raid
Part 8: How to Recover Data and Rebuild Failed Software RAIDs
Part 9: How to Manage Software RAIDs in Linux with Mdadm Tool
This is the Part 1 of a 9-tutorial series, here we will cover the introduction of
RAID, Concepts of RAID and RAID Levels that are required for the setting up
RAID in Linux.
Featured Concepts of RAID
Parity method in raid regenerate the lost content from parity
saved informations. RAID 5, RAID 6 Based on Parity.
Stripe is sharing data randomly to multiple disk. This wont
have full data in a single disk. If we use 3 disks half of our data
will be in each disks.
Mirroring is used in RAID 1 and RAID 10. Mirroring is making a
copy of same data. In RAID 1 it will save the same content to the
other disk too.
Hot spare is just a spare drive in our server which can
automatically replace the failed drives. If any one of the drive
failed in our array this hot spare drive will be used and rebuild
automatically.
Chunks are just a size of data which can be minimum from 4KB
and more. By defining chunk size we can increase the I/O
performance.
RAIDs are in various Levels. Here we will see only the RAID Levels which is
used mostly in real environment.
RAID0 = Striping
RAID1 = Mirroring
RAID5 = Single Disk Distributed Parity
RAID6 = Double Disk Distributed Parity
RAID10 = Combine of Mirror & Stripe. (Nested RAID)
RAID are managed using mdadm package in most of the Linux distributions.
Let us get a Brief look into each RAID Levels.
RAID 0 (or) Striping
Striping have a excellent performance. In Raid 0 (Striping) the data will be
written to disk using shared method. Half of the content will be in one disk and
another half will be written to other disk.
Let us assume we have 2 Disk drives, for example, if we write data
TECMINT to logical volume it will be saved as T will be saved in first disk
and E will be saved in Second disk and C will be saved in First disk and
again M will be saved in Second disk and it continues in round-robin process.
In this situation if any one of the drive fails we will loose our data, because
with half of data from one of the disk cant use to rebuilt the raid. But while
comparing to Write Speed and performance RAID 0 is Excellent. We need at
least minimum 2 disks to create a RAID 0 (Striping). If you need your valuable
data dont use this RAID LEVEL.
High Performance.
There is Zero Capacity Loss in RAID 0
Zero Fault Tolerance.
Write and Reading will be good performance.
RAID 1 (or) Mirroring
Mirroring have a good performance. Mirroring can make a copy of same data
what we have. Assuming we have two numbers of 2TB Hard drives, total there
we have 4TB, but in mirroring while the drives are behind the RAID Controller
to form a Logical drive Only we can see the 2TB of logical drive.
While we save any data, it will write to both 2TB Drives. Minimum two drives
are needed to create a RAID 1 or Mirror. If a disk failure occurred we can
reproduce the raid set by replacing a new disk. If any one of the disk fails in
RAID 1, we can get the data from other one as there was a copy of same
content in the other disk. So there is zero data loss.
Good Performance.
Here Half of the Space will be lost in total capacity.
Full Fault Tolerance.
Rebuilt will be faster.
Writing Performance will be slow.
Reading will be good.
Can be used for operating systems and database for small
scale.
RAID 5 (or) Distributed Parity
RAID 5 is mostly used in enterprise levels. RAID 5 work by distributed parity
method. Parity info will be used to rebuild the data. It rebuilds from the
information left on the remaining good drives. This will protect our data from
drive failure.
3
Assume we have 4 drives, if one drive fails and while we replace the failed
drive we can rebuild the replaced drive from parity informations. Parity
informations are Stored in all 4 drives, if we have 4 numbers of 1TB harddrive. The parity information will be stored in 256GB in each drivers and other
768GB in each drives will be defined for Users. RAID 5 can be survive from a
single Drive failure, If drives fails more than 1 will cause loss of datas.
Excellent Performance
Reading will be extremely very good in speed.
Writing will be Average, slow if we wont use a Hardware RAID
Controller.
Rebuild from Parity information from all drives.
Full Fault Tolerance.
1 Disk Space will be under Parity.
Can be used in file servers, web servers, very important
backups.
RAID 6 Two Parity Distributed Disk
RAID 6 is same as RAID 5 with two parity distributed system. Mostly used in a
large number of arrays. We need minimum 4 Drives, even if there 2 Drive fails
we can rebuild the data while replacing new drives.
Very slower than RAID 5, because it writes data to all 4 drivers at same time.
Will be average in speed while we using a Hardware RAID Controller. If we
have 6 numbers of 1TB hard-drives 4 drives will be used for data and 2 drives
will be used for Parity.
Poor Performance.
Read Performance will be good.
Write Performance will be Poor if we not using a Hardware RAID
Controller.
4
Rebuild from 2 Parity Drives.
Full Fault tolerance.
2 Disks space will be under Parity.
Can be Used in Large Arrays.
Can be use in backup purpose, video streaming, used in large
scale.
RAID 10 (or) Mirror & Stripe
RAID 10 can be called as 1+0 or 0+1. This will do both works of Mirror &
Striping. Mirror will be first and stripe will be the second in RAID 10. Stripe will
be the first and mirror will be the second in RAID 01. RAID 10 is better
comparing to 01.
Assume, we have 4 Number of drives. While Im writing some data to my
logical volume it will be saved under All 4 drives using mirror and stripe
methods.
If Im writing a data TECMINT in RAID 10 it will save the data as follow. First
T will write to both disks and second E will write to both disk, this step will
be used for all data write. It will make a copy of every data to other disk too.
Same time it will use the RAID 0 method and write data as follow T will write
to first disk and E will write to second disk. Again C will write to first Disk
and M to second disk.
Good read and write performance.
Here Half of the Space will be lost in total capacity.
Fault Tolerance.
Fast rebuild from copying data.
Can be used in Database storage for high performance and
availability.
Conclusion
5
In this article we have seen what is RAID and which levels are mostly used in
RAID in real environment. Hope you have learned the write-up about RAID.
For RAID setup one must know about the basic Knowledge about RAID. The
above content will fulfil basic understanding about RAID.
In the next upcoming articles Im going to cover how to setup and create a
RAID using Various Levels, Growing a RAID Group (Array) and
Troubleshooting with failed Drives and much more
