-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Hi Greg, On 28 Aug 2008, at 21:09, Greg Oster wrote:
I'm using 16384 and 2048 (it's the raid0g partition below that I'm testing with). - -bash-3.2# disklabel raid0 | grep Cyl a: 1048576 63 4.2BSD 0 0 0 # (Cyl. 0*- 1024*) b: 4194304 1048639 swap # (Cyl. 1024*- 5120*) d: 327679744 0 unused 0 0 # (Cyl. 0 - - 319999*) e: 16777216 5242943 4.2BSD 0 0 0 # (Cyl. 5120*- 21504*) f: 4194304 22020159 4.2BSD 0 0 0 # (Cyl. 21504*- 25600*) g: 301465281 26214463 4.2BSD 2048 16384 0 # (Cyl.^^^^^^^^ That offset is not a multiple of your stripe size (128 blocks)...
Umm.
That means that all filesystem blocks won't be stripe-aligned, and that's going to REALLY hurt you for write performance.. (you'll almost always be doing "small writes", as even a 64K write will get split over two different stripes :( ) This is somewhat old now, but here is a benchmark I did a few years back with w/ 64K block, 8K frag on a RAIDframe RAID 5 set of 5 disks: -------Sequential Output-------- ---Sequential Input-- --Random-- -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks--- MB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU /sec %CPU1500 86487 76.4 108263 70.5 10128 8.0 90153 74.4 141263 44.4 356.7 4.3I don't have a copy of the disklabel, but I suspect the filesystem began at block 0 of the RAID set... But it is possible to get good write speeds on RAID 5 with a bit of tuning :)
Ok, assuming that I basically always partition my disks (and RAID sets) the same way for convenience and that this means that I will start at offset 63 for reasons of PC MBRs and bootability.
Then I read what you're saying as "add ($stripsize - 63) extra blocks at the end of your 'a' partition before all the others". That way I ought to get all the remaining partitions stripe-aligned.
Will try that ASAP. Johan -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.5 (Darwin) iD8DBQFItwXAKJmr+nqSTbYRApbEAJ922qoxvx2s4Q1/qmnioRzRkA/LSwCgm2XT BTGcX9XHrdMU2EHiQqwtF+s= =6fUA -----END PGP SIGNATURE-----