On 8/5/2012 8:49 AM, Martin Steigerwald wrote: > Am Sonntag, 5. August 2012 schrieb 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. > > That does not match my memory, but I´d have to look it up. Maybe next > week. > > I am pretty sure mkfs.xfs on a single partition on a single harddisk upto > 2 TiB used 16 AGs for quite some time and now uses 4 AGs since quite some > time already. I think I have noted the exact xfsprogs version where it was > changed in my training slides. >From 'man mkfs.xfs' of xfsprogs 3.1.4 (probably not the latest) "The data section of the filesystem is divided into _value_ allocation groups (default value is scaled automatically based on the underlying device size)." It's not stated in man but the minimum is 4 AGs, unless that has changed in the last couple of years. This is what I was referring to previously when I stated 4 AGs is the default. What you likely did was format a 2TB device and saw 16 AGs due to the automatic scaling, then shortly thereafter formatted a much smaller device and saw the default minimum 4 AGs. Assuming agcount was statically defined, you assumed the default value had been decreased. -- Stan _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
