RAID config in diff DAE's in difff slots

Question

Hi

If I have the following empty slots in DAE0 slot 5-13, DAE1 slot 13-14, DAE2 slot 14, DAE4 slot 14, DAE6 slot 14 is it possible to create Raid Group from different DAE's in different slots.

For eg I want to create a RG of Raid5 4+1, I want to create on DAE0 slot5-9, another Raid5 4+1 on DAE0 slot 10-13 and DAE1 slot14.

Thanks

Allen Ward · Accepted Answer

Yes, it is very possible. Technically you can create a RAID group with drives from multiple different DAEs. You wouldn't necessarily want to do that because it becomes hard to track where your data is, but there is nothing preventing you from doing it.

The one thing you should be very careful about is ensuring that you are using similar drive types, and when you are crossing DAEs you will want to make sure that the DAEs are running at the same bus speed. The system won't prevent you from creating a RAID group on DAEs of multiple bus speeds, but you may not get the optimal performance if you mix and match.

And I'm going to assume that you are talking about DAEs with the same interface technology in them. You can't mix a RAID group across DAEs if one of them is FC and the other one is ATA (not really an issue on newer arrays, but have to be careful if you have older arrays with ATA drives/DAEs.

You should really take a look at the CLARiiON Best Practices for Fibre Channel Storage document for details on what you may or may not gain/lose and what the best practices are around array configuration. Excellent document and a good starting point for making the right decisions.

Allen Ward · Answer

Thanks Rob

I'm finding it harder and harder lately to actually get to questions in this particular forum before 2 or 3 other people have already chimed in. I'm not sure if I'm just "time zone challenged", or I have too #$%^ much work to do lately! *lol*

RRR · Answer

I couldn't have said it any better. 10 Points for Allen Ward

zainal1 · Answer

Hi Allen'I'm not sure why they left out slots 5-13 in DAE0'With regards to this, my colleague told me what EMC CE told him was 'What EMC explaind in the past was that there might cause performanceissue if we install data disk to DAE 0'I'm not sure how far this is true as all my CX have data disks on DAE0 besides the vault disks.

zainal1 · Answer

Hi AllenThanks.Your answer is very clear. All the disks are FC and a mixture of 146GB and 300GB.I'm not sure why they left out slots 5-13 in DAE0. Also if I may ask, can data disks be inter-mixed with vault disks. The array is a CX3-40 with R24. As to what was told to me by an EMC CE, for R26, it's possible and won't cause performance degradation.

kelleg · Answer

Remember that in addition to the differences in size, FC disks can also have different speeds - 10K or 15K - you probably would not want to mix different speed disks in the same Raid Group - the speed of the RG will be the slowest disk.

glen

Allen Ward · Answer

Data disks can definitely be mixed in the same DAE with the vault disks. I'm not sure why anyone would have suggested different, but I'd be suprised if you can find anyone else out there who isn't using all the slots in DAE 0_0. The recommendation is to avoid binding a RAID group that spans outside the vault/system drives. The system won't prevent it, but it is a best practice.

While most shops follow the best practice of not putting high IO load on the RAID group using drives 0_0_0 through 0_0_4, we take that one step further and reserve the space so it doesn't get used at all except for in emergencies. It is all up to how you can manage it at your site.

I just want to be clear from the other part of your note that the 146GB and 300GB drives are going to be in seperate RAID groups? If you were short one 146GB drive to complete a RAID group and had one spare 300GB that you didn't need as a hot spare it wouldn't hurt to use it, but if you bind RAID groups with multiple disk sizes you are effectively losing the extra capacity of the larger drives. (e.g. a RAID group of 1 x 146GB drive and 4 x 300GB drives would waste almost .5TB of usable space.

Allen Ward · Answer

Good point Glen,I was thinking about that when I started typing, but I guess it never got out of my head and into my post.

CLARiiON

RAID config in diff DAE's in difff slots

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