also sprach dean gaudet <dean@xxxxxxxxxx> [2006.11.03.2019 +0100]: > > I cannot find authoritative information about the relation between > > the RAID chunk size and the correct stride parameter to use when > > creating an ext2/3 filesystem. > > you know, it's interesting -- mkfs.xfs somehow gets the right sunit/swidth > automatically from the underlying md device. i don't know enough about xfs to be able to agree or disagree with you on that. > # mdadm --create --level=5 --raid-devices=4 --assume-clean --auto=yes /dev/md0 /dev/sd[abcd]1 > mdadm: array /dev/md0 started. with 64k chunks i assume... > # mkfs.xfs /dev/md0 > meta-data=/dev/md0 isize=256 agcount=32, agsize=9157232 > blks > = sectsz=4096 attr=0 > data = bsize=4096 blocks=293031424, imaxpct=25 > = sunit=16 swidth=48 blks, unwritten=1 sunit seems like the stride width i determined (64k chunks / 4k bzise), but what is swidth? Is it 64 * 3/4 because of the four device RAID5? > # mdadm --create --level=10 --layout=f2 --raid-devices=4 --assume-clean --auto=yes /dev/md0 /dev/sd[abcd]1 > mdadm: array /dev/md0 started. > # mkfs.xfs -f /dev/md0 > meta-data=/dev/md0 isize=256 agcount=32, agsize=6104816 blks > = sectsz=512 attr=0 > data = bsize=4096 blocks=195354112, imaxpct=25 > = sunit=16 swidth=64 blks, unwritten=1 okay, so as before, 16 stride size and 64 stripe width, because we're now dealing with mirrors. > # mdadm --create --level=10 --layout=n2 --raid-devices=4 --assume-clean --auto=yes /dev/md0 /dev/sd[abcd]1 > mdadm: array /dev/md0 started. > # mkfs.xfs -f /dev/md0 > meta-data=/dev/md0 isize=256 agcount=32, agsize=6104816 blks > = sectsz=512 attr=0 > data = bsize=4096 blocks=195354112, imaxpct=25 > = sunit=16 swidth=64 blks, unwritten=1 why not? in this case, -n2 and -f2 aren't any different, are they? > in a "near 2" layout i would expect sunit=16, swidth=32 ... but swidth=64 > probably doesn't hurt. why? > that's how i think it works -- i don't think ext[23] have a concept of "stripe > width" like xfs does. they just want to know how to avoid putting all the > critical data on one disk (which needs only the chunk size). but you should > probably ask on the linux-ext4 mailing list. once i understand everything... -- martin; (greetings from the heart of the sun.) \____ echo mailto: !#^."<*>"|tr "<*> mailto:"; net@madduck spamtraps: madduck.bogus@xxxxxxxxxxx if you find a spelling mistake in the above, you get to keep it.
Attachment:
signature.asc
Description: Digital signature (GPG/PGP)
