EVA4400 best practice versus reality

[Gerald Taylor]

Hello Guru's

I have an EVA4400 with 62x300GB FC and 8x1TB FATA disk. They are configured in two disk groups one with all the RC and one with all the FATA per best practices. I am adding 34x450GB FC disk (removing FATA because they turned out to be less useful than originally expected). The application is oracle 10g with raw volumes utilizing oracle ASM.
If I follow best practice I should create a second disk group with all the 450GB because they are the same size and speed. However, I understand that when it comes to performance it is best to have as many spindles as possible. I would prefer to put all the disk in one group and let the EVA work it out but I am curious if there are users out there who have tried mixing disks within one disk group and found it to be troublesome. I look forward to hearing from you.

Gerald

[IBaltay · Accepted solution]

Hi,
1. yes from the performance point of view it is not the optimum (not recommended) to have different sizes HDDs in one DG, also the disk protection (spare HDD) will be in the sizes of the "bigger" physical disks. However it is supported.
2. for Oracle, there is always the best practice to put redo and archive logs to the RAID1 with mirrors on the separate LUNs

[Uwe Zessin]

There isn't so much difference between 300 and 450 so that the larger disk does not draw much more I/O compared to other disk sizes, but you might silently lose disk group capacity over time if the EVA starts to pair 300/450GB disk drives during maintenance operations. The pairing is done to predefine the VRAID-1 members. In that case the capacity of the smaller disk drive is used for the pair.

The additional capacity required for 450GB disk drives in the group would be very little (300GB) compared to the total group size:
33,900GB - that is less than 1%.

[Gerald Taylor]

Thanks for the reply,

I think i will create a second disk group as the possibility of losing space could be an issue since we will have the maximum spindle count on this EVA. Thanks.

Gerald