[MSA1500] Array and Logicaldrives

[Luca Deboli]

Goodmorning everybody.
I'm setting up an MSA1500 with 10x300Gb SCSI drives.
Question is: i'd like to setup RAID 0+1 with 3x500Gb Luns (Vmware involved).
Should i create one single array and 3 logical 0+1 drives or three different arrays with a single logical drive each?
How can i be assured that data is used efficiently between all drives? Is there any best practices involved?
Thanks in advance for your kind replies

[Víctor Cespón · Accepted solution]

Option 1: 1 array with all 10 disks divided on 3 logical drives.
- Faster I/O because involves more drives
- Less security as there's more drives on the array (but RAID 1+0 is pretty safe, you'll have to loss two drives that are a mirror pair)

Option 2: 3 arrays (you need 4 drives per array for RAID 1+0, so that would need 2 more drives)
- Less performance, writes are stripped only on 2 disks (and their partners)
- More security, you can lose one disk on each RAID
- Separate traffic for each logical unit, more independent performance (limited by the speed of the FC link, obviusly)

[Luca Deboli]

Thank you Vcespon, i'd like to add a little question.
You can mix RAID logical drives into a single Array.
Is there any use of this or it's always a bad thing to do?
I think that mixing raids degrades performances, sorry but i'm a sort of newbie in SAN configurations :)

[Víctor Cespón]

Yes, you can join all the disks on a single RAID and then create several logical units, in RAID 0, RAID 1+0, RAID 5 or RAID 6. The type of RAID depends on the security and performance needed for the data.
Writes on RAID 5 or 6 take more I/Os, but you should first see if the total is too much for 10 disks.

For example, assuming a typical 60% reads, and 40% writes, with 10 disks you can expect 800 I/Os in RAID 1 and 500 in RAID 5 before latencies start to climb above 15 ms.

[marsh_1]

luca,

if you meant what impact does mixing different raid levels on the storage array have
i.e a raid 1 volume and a raid 5 volume (each of which can be split into further logical partitions). then yes it can impact performance from the point of view that it is usually faster to stripe data over as many spindles as possible given the available io channels on the storage array. with the finite resources you have (10 disks) any raid sub set will not perform quite as fast as using all 10 disks, but the difference should not be too big. it's always a balance between redundancy,performance and space requirements.

hope this helps

[Uwe Zessin]

c00622089 - Advisory: Degraded Read Performance with Multiple Logical Drives (LUNs) Configured to One Array Group with Specific Conditions

http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=c00622089