On Mon, Feb 7, 2011 at 7:53 PM, Richard Elling <richard.ell...@gmail.com> wrote:
> On Feb 7, 2011, at 1:07 PM, Peter Jeremy wrote:
>
>> On 2011-Feb-07 14:22:51 +0800, Matthew Angelo <bang...@gmail.com> wrote:
>>> I'm actually more leaning towards running a simple 7+1 RAIDZ1.
>>> Running this with 1TB is not a problem but I just wanted to
>>> investigate at what TB size the "scales would tip".
>>
>> It's not that simple. Whilst resilver time is proportional to device
>> size, it's far more impacted by the degree of fragmentation of the
>> pool. And there's no 'tipping point' - it's a gradual slope so it's
>> really up to you to decide where you want to sit on the probability
>> curve.
>
> The "tipping point" won't occur for similar configurations. The tip
> occurs for different configurations. In particular, if the size of the
> N+M parity scheme is very large and the resilver times become
> very, very large (weeks) then a (M-1)-way mirror scheme can provide
> better performance and dependability. But I consider these to be
> extreme cases.
Empirically it seems that resilver time is related to number of
objects as much (if not more than) amount of data. zpools (mirrors)
with similar amounts of data but radically different numbers of
objects take very different amounts of time to resilver. I have NOT
(yet) started actually measuring and tracking this, but the above is
based on casual observation.
P.S. I am measuring number of objects via `zdb -d` as that is faster
than trying to count files and directories and I expect is a much
better measure of what the underlying zfs code is dealing with (a
particular dataset may have lots of snapshot data that does not
(easily) show up).
--
{--------1---------2---------3---------4---------5---------6---------7---------}
Paul Kraus
-> Senior Systems Architect, Garnet River ( http://www.garnetriver.com/ )
-> Sound Coordinator, Schenectady Light Opera Company (
http://www.sloctheater.org/ )
-> Technical Advisor, RPI Players
_______________________________________________
zfs-discuss mailing list
zfs-discuss@opensolaris.org
http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
