[zfs-discuss] Improving snapshot write performance

Ian Collins
2012-04-12T04:21:25Z

On 04/12/12 09:00 AM, Jim Klimov wrote:
> 2012-04-11 23:55, Ian Collins wrote:
>> Odd. The pool is a single iSCSI volume exported from a 7320 and there
is
>> 18TB free.
> Lame question: is that 18Tb free on the pool inside the
> iSCSI volume, or on the backing pool on 7320?
>
> I mean that as far as the "external" pool is concerned,
> the zvol''s blocks are allocated - even if the "internal"
> pool considers them deleted but did not zero them out
> and/or TRIM them explicitly.
>
> Thus there may be lags due to fragmentation on the backing
> "external" pool (physical on 7320), especially if it is
> not very free and/or ifs free space is already too heavily
> fragmented into many small "bubbles".

I''ll check, but I see the same effect with local replications as well.

--
Ian.