reallocating deduped volumes in 8.1

[rajdeepsengupta]

As a part of 8.1 feature list, I found that you can reallocate dedup volume as well, using -p option. But my question is, is it a good idea to reallocate all the volumes in the filer using regular reallocate schedules, or we can use some mechanism to see which all volumes are not evenly distributed across the aggr disks. To view it, the crude method would be to look into the statit disk load. But is there any other way to see which volumes need proper reallocation?

Also when we add disks to an existing aggr, we should reallocate, but for deduped volumes should we use -f -p option, I am need some expert guidance on this.

Thanks in advance

[radek_kubka]

Hi,

You can measure the level of fragmentation using reallocate command.

Reallocating deduped volumes is a new thing & I still can't get my head around how it may possibly improve things (if the same block is shared between multiple files, which file wins to be contiguous, if you know what I mean?)

There is plenty of different info about reallocate in this thread:

https://communities.netapp.com/message/37584#37584

Regards,
Radek

[rajdeepsengupta]

Yes, I have read this thread, which is pretty old one.

Earlier consensus was that you should only reallocate physical blocks using -f option for normal volumes, and avoid it for dedup volume, because for dedup volumes it may decrease the performance for obvious reason.

But with Ontap 8.1, there seems some major technical change in the way Ontap handles duplication, as a result you can do reallocate safely.

So, I have two questions:

1. What is that major change in Ontap, which made possible to reallocate dedup volumes without any performance impact?

2.I agree that it is safe to measure the level of fragmentation, but what I do if I have added disk on the aggregate, I mean than I am force to reallocate, else I won't get the benefit of additional spindles for performance, but my voluems are deduped?

Thanks