Maybe I'm missing something, but I'm not sure how the information below
maps to setting the values on Hardware RAID.
A nice feature of xfs is that it's intelligent enough to figure out the
proper values for SW RAID.
Thanks!
Shailendra Tripathi wrote:
For RAID-5 device, for any write, the parity as well has to be
calculated before writing. In absence of any column of RAID, it is
read from disk and then re-written. When you choose writes such as all
columns are already there, parity can be directly calculated and
written (without incurring any extra read I/O) and that's why,
declaring in that form is desirable. Someone correct me if I am wrong.
# mdadm --create /dev/md15 --level=5 --raid-devices=3 -c 64 /dev/sd[hvi]1
mdadm: array /dev/md15 started.
When forced choice of sw=1,su=128k
# cat /proc/mdstat | more
...
md15 : active raid5 sdv1[2] sdi1[1] sdh1[0]
78139904 blocks level 5, 64k chunk, algorithm 2 [3/3] [UUU]
# mkfs.xfs -f -d sw=1,su=128k /dev/md15
mkfs.xfs: Specified data stripe unit 256 is not the same as the volume
stripe unit 128
meta-data=/dev/md15 isize=256 agcount=16,
agsize=1220928 blks
= sectsz=512
data = bsize=4096 blocks=19534848, imaxpct=25
= sunit=32 swidth=32 blks, unwritten=1
naming =version 2 bsize=4096
log =internal log bsize=4096 blocks=9568, version=1
= sectsz=512 sunit=0 blks
realtime =none extsz=131072 blocks=0, rtextents=0
Though by default, it detects the former one.
# mkfs.xfs -f /dev/md15
meta-data=/dev/md15 isize=256 agcount=16,
agsize=1220944 blks
= sectsz=512
data = bsize=4096 blocks=19534976, imaxpct=25
= sunit=16 swidth=32 blks, unwritten=1
naming =version 2 bsize=4096
Please note that default created here is: sunit=16, swidth=3
bridavis@xxxxxxxxxxx wrote:
I getting conflicting reports as to how I should generate my
sunit/swidth vaules for hardware RAID 5.
Setup: hardware RAID 5, 3 disks at 300 GBs each, 64k stripe size.
Originally, following the man page and the mailing list archives, I
came up sw=2,su=64k.
However, I read a reply to an earlier question I sent to the list,
and it indicated that the hardward RAID should be treated as a single
disk, so I came up with sw=1,su=128k.
Which one is correct for my setup?
Thanks!
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