On 7/13/13 11:20 PM, aurfalien wrote: > > On Jul 13, 2013, at 7:13 PM, Eric Sandeen wrote: > >> 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? > > Autodesk has this software called Flame which requires very very fast > local storage using XFS. They have an entire write up on how to calc > proper agsize for optimal performance. http://wikihelp.autodesk.com/Creative_Finishing/enu/2012/Help/05_Installation_Guides/Installation_and_Configuration_Guide_for_Linux_Workstations/0118-Advanced118/0194-Manually194/0199-Creating199 I guess? That's quite a procedure! And I have to say, a slightly strange one at first glance. It'd be nice if they said what they were trying to accomplish rather than just giving you a long recipe. In the end, I think they are trying to create 128AGs and maybe work around some mkfs corner case or other. > I never mess with agsize but it is require when creating the XFS > file system for use with Flame. I realize its tailored for there > apps particular IO characteristics, so I'm curious about it. In general more AGs allow more concurrency for some operations; it also will generally change how/where files in multiple directories get allocated. >>> 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. > > Well, it will give me a base line comparison of non tweaked agsize vs tweaked agsize. Not necessarily, see above; I'm not sure what iozone invocation would show any effects from more or fewer AGs. Anyway, iozone != flame, not by a long shot! :) >>> 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. ;) > > Yea but based on what? > > Why 32 at there current size? see calc_default_ag_geometry() Since you are in multidisk mode (you have stripe geometry) it uses more AGs for more AGs since it knows you have more spindles: } else if (dblocks > GIGABYTES(512, blocklog)) shift = 5; 2^5 = 32 If you hadn't been in multidisk mode you would have gotten 25 AGs due to the max AG size of 1T. >>> 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 > > Problem is I run Centos so the line; > > "As of kernel 3.2.12, the default i/o scheduler, CFQ, will defeat much of the parallelization in XFS. " > > ... doesn't really apply. Well, my point was that your original question, "are these optimal numbers?" included absolutely no context of your workload, so the best answer is yes - the default mkfs behavior is optimal for a generic, unspecified workload. I don't have access to Autodesk Flame so I really don't know how it behaves or what an optimal tuning might be. Anyway, I think the calc_default_ag_geometry() info above answered your original question of "why does XFS think I have 32 allocation groups with the corresponding size?" - that's simply the default mkfs algorithm when in multidisk mode, for a disk of this size. -Eric _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
