[geeks] Choice of filesystem for /var

[Charles Shannon Hendrix]

Thu, 19 Oct 2006 @ 15:32 -0400, Francois Dion said:

> > Personally I would not use zfs, but rather a stripped down ufs with any
> > non-essential metadata turned off for speed.  Tune it for your most
> > common files, if you think you need it.
> >
> > I don't think the overhead of zfs is worth it.

Just a clarification... I was thinking of a traditional /var where you
rarely depend on the data.

If you depend on the data, then a journaled FS makes sense.

It's just that /var is often the site of a lot of temp activity, and you
will pay a performance price there which is often higher than for other
common mount points.

> > It does lead to a question for the ZFS experts though: can you turn
> > things like atime modification off in ZFS and if so, does it gain a lot
> > of speed like it does for other filesystems?
> 
> zfs set atime=off pool/log
> 
> You gain the same as any other. But much more than this, if it's a log
> and in text format, setting compression=on dwarfs everything else.

You mean that it saves time in addition to space?

Mostly I was talking about the clouds of temp files that can populate
var depending on the apps you run.

> There are 25 properties in all that can be set similarly. Then there
> is stuff like vq_max_pending, vdev_prefetch etc..

I was hearing a few people awhile back complaining a lot about ZFS with
temporary files, but it seems that should just be a matter of tuning as
long as ZFS overhead is acceptable. You rarely really need atime, and
there are probably other meta updates that can be turned off. Disabling
all access control should help a lot. I hate it when filesystems have
ACLs, but you can't disable them when you don't need them.

Truth is, most people still don't tune their filesystems, even though it
can make a big difference.

Even desktop software is getting really heavy in the "create massive
numbers of temp files" department.

> If you want to figure out what is the compression ratio: zfs get
> compressratio pool/log
> 
> My oracle home with all the binary stuff still compresses 1.6x,
> surprisingly.

I'm still pretty nervous about compressing filesystems, even though it
can be nice.



-- 
shannon "AT" widomaker.com -- ["We have nothing to prove" -- Alan Dawkins]