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Vraid1 and Vraid5

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simon_164
Super Advisor

Vraid1 and Vraid5

I have always tried not to mix Vraid1 and Vraid5 within the same diskgroup. because of the difference in Chunk sizes. Do you think this is a good strategy, or it doesn't matter in EVA?
Sometimes I am forced to use only one diskgroup because of the advantages of disk space and ....
What happens to the performance when Vraid1 and Vraid5 are mixed within the same diskgroup?
4 REPLIES
Amar_Joshi
Honored Contributor
Solution

Re: Vraid1 and Vraid5

Hi Simon,

I don't know how you found out about different chunk size, in my opinion EVA virtualize this feature and prevents user to configure it.

The 2 major differences I can tell you are:

1. You have more chances to loose whole VDisk when one of the disks fails in DiskGroup.

2. Performance is better in RAID0 because it has less data to write compare to RAID5 (it has parity) and RAID5 has overhead of creating the parity using the RAID5 algorithm.

Hope this helps.
Uwe Zessin
Honored Contributor

Re: Vraid1 and Vraid5

All VRAID levels use the same chunk size (128 KBytes).

It is hard to make blank performance statements. Imagine this:
- assume an aligned 4-chunk write
-- VRAID-1 needs to write out 8 chunks (4D+4D)
-- VRAID-5 calculates the parity chunk and writes out 5 chunks (4D+P)
.
Peter Mattei
Honored Contributor

Re: Vraid1 and Vraid5

Statistically it is better using large diskgroups with a mix of R1 and R5 than having multiple dedicated DGs per Raid level.

Assume you have 80 disks in one DG; all LUNs are striped across all 80 disks, IOs are optimally disributed and all disks are equally busy.

If you divide the same 80 disks into 2x 40 disk DGs there is a higher chance for inbalance since either the R1 or the R5 DG is more busy and you cannot utilize the full available backend performance!

So as a rule of thumb: less but larger DG are better for performance!

Cheers
Peter
I love storage
simon_164
Super Advisor

Re: Vraid1 and Vraid5

Thanks all,

I once had an EVA training and the instructor insisted many times not to mix Vraid1 and Vraid5 within the same Disk Group. Obviously he was wrong, always double check your sources. Well from now on, m gonna follow the instructions for best performance, specially if i have different disk sizes and speed and types.

Thank you!!