Question about RAID

[Shazzum]

Hey I'm new to all this, could someone please tell me the difference between RAID level 5 and RAID level 0+1, cause the way that I look at it they both do the same thing. I'm a newbie though so I'm sure I'm missing something.

 

[qeru]

http://www.anandtech.com/storage/showdoc.html?i=1491
or, AnandTech Home > Storage section > IDE RAID Comparison

 

[Jhereg]

RAID 5 requires at least 3 drives .
:Ripped from adaptec site beacuse I'm too lazy:

RAID Level 5
This level is commonly referred to as striping with distributed parity.
RAID Level 5 is similar to level 4, but distributes parity among the drives.
No single disk is devoted to parity. This can speed small writes in multiprocessing systems.

::Ripped from the Mylex site :::

RAID 0+1 is a Mylex standard, Adaptec uses 0/1

RAID 0+1 is a combination of RAID levels 0 and 1 that provides enhanced data availability through disk mirroring and increased I/O performance through disk striping. The advantages are faster data access, due mainly to the RAID 0 feature, and fault tolerance to disk failure, a consequence of the RAID 1 attribute. In the Mylex RAID 0+1 implementation, data availability is maintained even if up to half of the hard disks fail, provided that such disks are non-adjacent members in the array.
Mylex?s RAID 0+1 provides interleaved mirroring, which allows the flexibility for both even and odd numbers of hard disks in an array. Adaptec?s RAID 0/1 is limited to only an even number of hard disks. Mylex RAID 0+1 may be simultaneously used with other RAID levels in an array. For example, both RAID 5 and RAID 0+1 logical disks may co-exist within the same array. However, Adaptec requires dedicated RAID 1 drive pairs within the array, thereby disallowing RAID levels to be intermixed. Providing a cost-effective solution for users, Mylex RAID 0+1 may be configured with as few as three drives. Adaptec requires a minimum of four drives for their RAID 0/1. Both RAID level implementations support a maximum of sixteen hard disks


The adavantage of both RAID 5 and 1+0 ,0/1 is that if there is a single drive failure, you can rebuild without a loss of data ( trust me .. I've had that happen)

The advantage of RAID 0+1/, 0/1 is that you get the performance of a RAID 0 ( striped array ) with the redundancy of RAID 1 ( mirrored array)

The disadvantage is the amount of drives needed for the redundancy : For example, if you have 4 20GB drives , with a 0+1 only 40 GB will be available, the left taken up by the mirrors.

RAID 5 advantage is you can have more drive capacity: With the same 4 20GB drives you have a total of 80 GB available.

The disadvantage of RAID 5 is that it is slower than a RAID 0+1 array.


For Reading Pleasure :



Mylex

Adaptec

 

[Raven76]

"RAID 5 advantage is you can have more drive capacity: With the same 4 20GB drives you have a total of 80 GB available."

Just to keep things clear, In that case you would have 80GB of space, but only 60GB available. The other 20GB is used for the parity bits. 1 drive in a RAID 5 array is always used to store parity and is therefore lost storage space. BTW: the calculation and writing of parity bits is also what decreases the write performance of a RAID 5 array since it takes more time to write the parity to the disk array.

 

[ChrisIsBored]

1 drive in a RAID 5 array is always used to store parity and is therefore lost storage space.

Actually, in RAID 5 the parity is striped across all of the drives. In RAID 3 the parity is stored in one single drive.

 

[Jhereg]

<< "RAID 5 advantage is you can have more drive capacity: With the same 4 20GB drives you have a total of 80 GB available."

Just to keep things clear, In that case you would have 80GB of space, but only 60GB available. The other 20GB is used for the parity bits. 1 drive in a RAID 5 array is always used to store parity and is therefore lost storage space. BTW: the calculation and writing of parity bits is also what decreases the write performance of a RAID 5 array since it takes more time to write the parity to the disk array. >>



Brain Fart on my end .. I meant to say 60GB.. need more coffee I guess...