On Mon, Aug 30, 2010 at 03:56:42PM -0700, Richard Elling wrote: > comment below... > > On Aug 30, 2010, at 3:42 PM, Ray Van Dolson wrote: > > > On Mon, Aug 30, 2010 at 03:37:52PM -0700, Eric D. Mudama wrote: > >> On Mon, Aug 30 at 15:05, Ray Van Dolson wrote: > >>> I want to "fix" (as much as is possible) a misalignment issue with an > >>> X-25E that I am using for both OS and as an slog device. > >>> > >>> This is on x86 hardware running Solaris 10U8. > >>> > >>> Partition table looks as follows: > >>> > >>> Part Tag Flag Cylinders Size Blocks > >>> 0 root wm 1 - 1306 10.00GB (1306/0/0) 20980890 > >>> 1 unassigned wu 0 0 (0/0/0) 0 > >>> 2 backup wm 0 - 3886 29.78GB (3887/0/0) 62444655 > >>> 3 unassigned wu 1307 - 3886 19.76GB (2580/0/0) 41447700 > >>> 4 unassigned wu 0 0 (0/0/0) 0 > >>> 5 unassigned wu 0 0 (0/0/0) 0 > >>> 6 unassigned wu 0 0 (0/0/0) 0 > >>> 7 unassigned wu 0 0 (0/0/0) 0 > >>> 8 boot wu 0 - 0 7.84MB (1/0/0) 16065 > >>> 9 unassigned wu 0 0 (0/0/0) 0 > >>> > >>> And here is fdisk: > >>> > >>> Total disk size is 3890 cylinders > >>> Cylinder size is 16065 (512 byte) blocks > >>> > >>> Cylinders > >>> Partition Status Type Start End Length % > >>> ========= ====== ============ ===== === ====== === > >>> 1 Active Solaris 1 3889 3889 100 > >>> > >>> Slice 0 is where the OS lives and slice 3 is our slog. As you can see > >>> from the fdisk partition table (and from the slice view), the OS > >>> partition starts on cylinder 1 -- which is not 4k aligned. > > To get to a fine alignment, you need an EFI label. However, Solaris does > not (yet) support booting from EFI labeled disks. The older SMI labels > are all "cylinder" aligned which gives you a 1/4 chance of alignment.
Yep... our other boxes similar to this one are using whole disks as ZIL, so we're able to use EFI. The Device Not Ready errors happen there too (SSD's are on an expander) but only from between 5-15 errors per day (vs the 500 per hour on the split OS/slog setup). > > >>> > >>> I don't think there is much I can do to fix this without reinstalling. > >>> > >>> However, I'm most concerned about the slog slice and would like to > >>> recreate its partition such that it begins on cylinder 1312. > >>> > >>> So a few questions: > >>> > >>> - Would making s3 be 4k block aligned help even though s0 is not? > >>> - Do I need to worry about 4k block aligning the *end* of the > >>> slice? eg instead of ending s3 on cylinder 3886, end it on 3880 > >>> instead? > >>> > >>> Thanks, > >>> Ray > >> > >> Do you specifically have benchmark data indicating unaligned or > >> aligned+offset access on the X25-E is significantly worse than aligned > >> access? > >> > >> I'd thought the "tier1" SSDs didn't have problems with these workloads. > > > > I've been experiencing heavy Device Not Ready errors with this > > configuration, and thought perhaps it could be exacerbated by the block > > alignment issue. > > > > See this thread[1]. > > > > So this would be a troubleshooting step to attempt to further isolate > > the problem -- by eliminating the 4k alignment issue as a factor. > > In my experience, port expanders with SATA drives do not handle > the high I/O rate that can be generated by a modest server. We are > still trying to get to the bottom of these issues, but they do not appear > to be related to the OS, mpt driver, ZIL use, or alignment. > -- richard Very interesting. We've been looking at Nexenta as we haven't been able to reproduce our issues on OpenSolaris -- I was hoping this meant NexentaStor wouldn't have the issue. In any case -- any thoughts on whether or not I'll be helping anything if I change my slog slice starting cylinder to be 4k aligned even though slice 0 isn't? > > > > > Just want to make sure I set up the alignment as optimally as possible. > > > > Ray > > > > [1] http://markmail.org/message/5rmfzvqwlmosh2oh Thanks, Ray _______________________________________________ zfs-discuss mailing list zfs-discuss@opensolaris.org http://mail.opensolaris.org/mailman/listinfo/zfs-discuss
