xfs_growfs / planned resize / performance impact

[Stan Hoeppner]

On 8/5/2012 6:03 AM, Martin Steigerwald wrote:

> Well the default was 16 AGs for volumes < 2 TiB AFAIR. And it has been 
> reduced to 4 for as I remember exactly performance reasons. Too many AGs 
> on a single device can incur too much parallelity. Thats at least is what 
> I have understood back then.

For striped md/RAID or LVM volumes mkfs.xfs will create 16 AGs by
default because it reads the configuration and finds a striped volume.
The theory here is that more AGs offers better performance in the
average case on a striped volume.

With hardware RAID or a single drive, or any storage configuration for
which mkfs.xfs is unable to query the parameters, mkfs.xfs creates 4 AGs
by default.  The 4 AG default has been with us for a very long time.  It
was never reduced.

-- 
Stan