On Wed, 23 Apr 2008 14:57:35 -0600 Andreas Dilger <adilger@xxxxxxx> wrote: > On Apr 22, 2008 14:57 -0400, Theodore Ts'o wrote: > > On Tue, Apr 22, 2008 at 10:32:12AM -0500, Jose R. Santos wrote: > > > I see that now, guess I should not read code with out having > > > breakfast. I think 8 is a very safe and conservative number, maybe to > > > conservative. The 64 group packing was the number I found to be a > > > overall improvement with the limited number of drives that I had to > > > test with. Haven't done any testing on old drives or laptop drive with > > > slow spindle speed but I would think 16 or 32 would be safe here unless > > > the drive is really old and small. > > > > Let's stay with 16 then for now. Spindle speed doesn't actually > > matter here; what matters is seek speed, and the density of the disk > > drive. The other thing which worries me though is that the size of > > each flex_bg block group cluster is dependent on the size of the block > > group, which in turn is related to the square of the filesystem > > blocksize. i.e., assuming a fs blockgroup size of 16, then: > > > > Blocksize Blocks/blockgroup Blockgroup Size Flex_BG cluster size > > > > 1k 8192 8 Meg 128 Meg > > 2k 16384 32 Meg 512 Meg > > 4k 32768 128 Meg 2 Gig > > 8k 65536 512 Meg 8 Gig > > 16k 131072 2 Gig 32 Gig > > 32k 262144 8 Gig 128 Gig > > 64k 524288 32 Gig 512 Gig > > > > So using a fixed default of 16, the flexible blockgroup size can range > > anything from 128 megs to half a terabyte! > > > > How much a difference in your numbers are you seeing, anyway? Is it > > big enough that we really need to worry about it? > > It probably makes sense to change the mke2fs/tune2fs parameter to be in > MB or GB instead of a count of groups, and/or change the internal default > to be a function of the groups size instead of just a constant. Did you mean making it a function of the block size? I agree that this would make more sense than just the constant. > Cheers, Andreas > -- > Andreas Dilger > Sr. Staff Engineer, Lustre Group > Sun Microsystems of Canada, Inc. > -JRS -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
