Re: Efficient way to import snapshots?

From: Craig Boston <craig@olyun.gank.org>
Date: Jul 31, 2007, 13:53 UTC
Message-ID: <20070731135332.GA58867@nowhere>
In-Reply-To: <20070731042347.GG25876@thunk.org>

On Tue, Jul 31, 2007 at 12:23:47AM -0400, Theodore Tso wrote:

> On Mon, Jul 30, 2007 at 06:44:13PM -0700, Linus Torvalds wrote:
> > 
> > Oh, ok. Solaris.

For reference, as I mentioned to Linus & Junio in an excessively verbose, and probably uninteresting to most of the git-list members, message about the performance characteristics of ZFS, I'm actually running FreeBSD-current with the experimental port of ZFS.

So, even less tested & tuned than it is on Solaris. Part of what I'm doing is stress testing the filesystem on machines with less than the recommended memory. Even if performance is suboptimal, it should at least not break anything.

> Craig, it might be interesting to see what sort of results you get if
> you use UFS instead of ZFS in your low-memory constrained
> environment...

I just so happen to be rebuilding the zfs pool on that server this morning in order to add more swap, so your wish(1tcl) is my rcmd(3).

Same machine, on a UFS filesystem (single disk, since zfs was doing the RAID), with the cache tuning parameters reset back to defaults:

First 'git status' after a reboot: git status 2.23s user 2.23s system 17% cpu 24.987 total

Second: git status 1.81s user 1.34s system 98% cpu 3.188 total

Third: git status 1.76s user 1.45s system 98% cpu 3.252 total

So I definitely think the problem is just that with its increased overhead, ZFS simply can't keep all the metadata in the cache with the available memory.

Craig