Re: swidth with mdadm and RAID6

Steve Cousins
2006-09-18T15:34:30Z

Hi Shailendra,

Here is the info:

1. [root@juno ~]# cat /proc/mdstat
Personalities : [raid6]
md0 : active raid6 sdb[0] sdl[10](S) sdk[9] sdj[8] sdi[7] sdh[6] sdg[5]
sdf[4] sde[3] sdd[2] sdc[1]
3907091968 blocks level 6, 64k chunk, algorithm 2 [10/10]
[UUUUUUUUUU]

unused devices: <none>

2. mdadm --create /dev/md0 --chunk=64 --level=6 --raid-devices=10
--spare-devices=1 /dev/sd[bcdefghijkl]

3. [root@juno ~]# xfs_db -r /dev/md*
xfs_db> sb
xfs_db> p
magicnum = 0x58465342
blocksize = 4096
dblocks = 976772992
rblocks = 0
rextents = 0
uuid = 04b32cce-ed38-496f-811f-2ccd51450bf4
logstart = 536870919
rootino = 256
rbmino = 257
rsumino = 258
rextsize = 144
agblocks = 30524160
agcount = 32
rbmblocks = 0
logblocks = 32768
versionnum = 0x3d84
sectsize = 4096
inodesize = 256
inopblock = 16
fname = "\000\000\000\000\000\000\000\000\000\000\000\000"
blocklog = 12
sectlog = 12
inodelog = 8
inopblog = 4
agblklog = 25
rextslog = 0
inprogress = 0
imax_pct = 25
icount = 36864
ifree = 362
fdblocks = 669630878
frextents = 0
uquotino = 0
gquotino = 0
qflags = 0
flags = 0
shared_vn = 0
inoalignmt = 2
unit = 16
width = 144
dirblklog = 0
logsectlog = 12
logsectsize = 4096
logsunit = 4096
features2 = 0
xfs_db>

Thanks for the help.

Steve

______________________________________________________________________
Steve Cousins, Ocean Modeling Group Email: cousins@umit.maine.edu
Marine Sciences, 452 Aubert Hall http://rocky.umeoce.maine.edu
Univ. of Maine, Orono, ME 04469 Phone: (207) 581-4302

On Mon, 18 Sep 2006, Shailendra Tripathi wrote:

> Can you list the output of
> 1. cat /proc/mdstat
> 2. the command to create 8+2 RAID6 with one spare ?
> 3. and output of following:
> xfs_db -r /dev/md*
> xfs_db> sb
> xfs_db> p
>
> -shailendra
>
> Steve Cousins wrote:
> >> I have a RAID6 array of 11 500 GB drives using mdadm. There is one
> >> hot-spare so the number of data drives is 8. I used mkfs.xfs with
> >> defaults to create the file system and it seemed to pick up the chunk size
> >> I used correctly (64K) but I think it got the swidth wrong. Here is what
> >> xfs_info says:
> >>
> >> ===========================================================================
> >> meta-data=/dev/md0 isize=256 agcount=32, agsize=30524160
> >> blks
> >> = sectsz=4096 attr=0
> >> data = bsize=4096 blocks=976772992, imaxpct=25
> >> = sunit=16 swidth=144 blks, unwritten=1
> >> naming =version 2 bsize=4096
> >> log =internal bsize=4096 blocks=32768, version=2
> >> = sectsz=4096 sunit=1 blks
> >> realtime =none extsz=589824 blocks=0, rtextents=0
> >> ===========================================================================
> >>
> >> So, sunit*bsize=64K, but swidth=144 and swidth/sunit=9 so it looks like it
> >> thought there were 9 data drives instead of 8.
> >>
> >> Am I diagnosing this correctly? Should I recreate the array and
> >> explicitly set sunit=16 and swidth=128?
> >>
> >> Thanks for your help.
> >>
> >> Steve
> >> ______________________________________________________________________
> >> Steve Cousins, Ocean Modeling Group Email: cousins@umit.maine.edu
> >> Marine Sciences, 452 Aubert Hall http://rocky.umeoce.maine.edu
> >> Univ. of Maine, Orono, ME 04469 Phone: (207) 581-4302
> >>
> >>
> >
>