Nathan Scott wrote:
On Thu, Feb 03, 2005 at 04:50:34PM -0800, David Sparks wrote:
I'm setting up a SAN with a 1TB partition and am seeking some advice.
Previously when setting up servers, I would specify options to mkfs.xfs
to lower the agcount and create a 32m log, ie for a 33GB partition:
mkfs.xfs -d agcount=32 -l size=32m /dev/sda3
This was based on an article I read at:
http://www-106.ibm.com/developerworks/linux/library/l-fs10.html
Aha, thats whos been telling people that! The article is a bit
out of date now.
More recently I've not bothered with those options because I read
somewhere that the defaults are sane. (I've never noticed any
difference either way) Are the mkfs.xfs defaults good for a 1TB partition?
Yes, should be just fine. In fact, from a quick check, current
mkfs will create a 32 AG filesystem on a 1Terabyte device...
# mkfs.xfs -N -dfile,size=1t,name=/dev/null
meta-data=/dev/null isize=256 agcount=32, agsize=8388608 blks
...
This didn't make any sense to me until I noticed this change in the manpage:
man mkfs.xfs used to say:
> The minimum allocation group size
> is 16 MB; the maximum size is just under 4 GB.
now it says:
> The minimum allocation group size
> is 16 MiB; the maximum size is just under 1 TiB.
(max ag size went from 4 GB to 1 TiB)
So I would agree that the original article is now out of date in regards
to mkfs.xfs suggestions.
Nobody commented on this question though, I'll put it up again. Most of
the information I've gathered on external logs dates back to the IRIX
days -- I hope there isn't anything out of date there.
> Regarding external logs, I've never formatted a XFS with an external
> log. From what I can gather (google, man pages), doing so is supposed
> to reduce disk head seeking hence performance is improved. Is anyone
> aware of any benchmarks that explore internal/external logs and sizes?
> My preference is for an internal log as that just simplifies things.
Is there any advantage to an external log on a separate partition on the
same device, as opposed to an external log on a separate device?
Basically is an external log only for performance benefits or are there
robustness benefits also?
Cheers!
ds
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