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Re: UFS performance oddities

On Fri, September 7, 2012 5:23 am, Steven Chamberlain wrote:
> Hi,
> On 07/09/12 11:55, David Given wrote:
>> My suspicion is that there's something cache-related with the SSD, in
>> that it's doing all metadata writes synchronously. Perhaps the SSD
>> doesn't support write barriers?
> Plain UFS could be expected to be slow.  Because it is unjournalled, I
> think metadata updates are forced to be synchronous.

I have PC-BSD mounted on UFS on an old Compaq nx6120 laptop and it is
anything other than slow. System updates are slow, but that has got more
to do with the packaging mechanism than anything else.
> The `camcontrol identify ada0` command should show the status of a
> disk's write cache (and sysctl hw.ata.wc must also be 1).  I think it
> will be 'on', but the sync updates of metadata might mean it is flushed
> regularly.
> It sounds like soft updates would help with this:
> http://www.freebsd.org/doc/handbook/configtuning-disk.html#SOFT-UPDATES
> On Debian GNU/kFreeBSD the tunefs binary from ufsutils is instead called
> tunefs.ufs
> If it is true that upstream FreeBSD 9.0 now enable softupdates by
> default, perhaps we should have done the same.  But now is probably too
> late.
> I think ideally this would be selectable during install, defaulting to
> 'on' (and that could be implemented around the same time as installer
> support for selecting ZFS options e.g. compression/noatime/copies/dedup
> ;).
> ZFS should of course be unaffected by the above issue, and be the
> best-performing choice of filesystem here.

ZFS is no advantage unless you have a minimum of 4 GB of RAM and a 64 Bit
system. It does have excellent management tools.


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