Re: specify agsize?

Eric Sandeen
2013-07-14T02:13:11Z

On 7/13/13 7:11 PM, aurfalien wrote:
> Hello again,
>
> I have a Raid 6 x16 disk array with 128k stripe size and a 512 byte block size.
>
> So I do;
>
> mkfs.xfs -f -l size=512m -d su=128k,sw=14 /dev/mapper/vg_doofus_data-lv_data
>
> And I get;
>
> meta-data=/dev/mapper/vg_doofus_data-lv_data isize=256 agcount=32, agsize=209428640 blks
> = sectsz=512 attr=2, projid32bit=0
> data = bsize=4096 blocks=6701716480, imaxpct=5
> = sunit=32 swidth=448 blks
> naming =version 2 bsize=4096 ascii-ci=0
> log =internal log bsize=4096 blocks=131072, version=2
> = sectsz=512 sunit=32 blks, lazy-count=1
> realtime =none extsz=4096 blocks=0, rtextents=0
>
>
> All is fine but I was recently made aware of tweaking agsize.

Made aware by what? For what reason?

> So I would like to mess around and iozone any diffs between the above
> agcount of 32 and whatever agcount changes I may do.

Unless iozone is your machine's normal workload, that will probably prove to be uninteresting.

> I didn't see any mention of agsize/agcount on the XFS FAQ and would
> like to know, based on the above, why does XFS think I have 32
> allocation groups with the corresponding size?

It doesn't think so, it _knows_ so, because it made them itself. ;)

> And are these optimal
> numbers?

How high is up?

Here's the appropriate faq entry:

http://xfs.org/index.php/XFS_FAQ#Q:_I_want_to_tune_my_XFS_filesystems_for_.3Csomething.3E

-Eric

> Thanks in advance,
>
> - aurf
>
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