Re: swidth with mdadm and RAID6

Shailendra Tripathi
2006-09-18T18:20:26Z

Hi Steve,
Both of us are using old xfsprogs. It is handled in new
xfsprogs.

*/
switch (md.level) {
case 6:
md.nr_disks--;
/* fallthrough */
case 5:
case 4:
md.nr_disks--;
/* fallthrough */
case 1:
case 0:
case 10:
break;
default:
return 0;

Regards,

Shailendra Tripathi wrote:

> Hi Steve,
> I checked the code and it appears that XFS is not *aware*
> of RAID6. Basically, for all md devices, it gets the volume info by
> making a an ioctl call. I can see that XFS only take care of level 4
> and level 5. It does not account for level 6.
> Only extra line need to be added here as below:
>
> if (md.level == 6)
> md.nr_disks -= 2; /* RAID 6 has 2 parity disks */
> You can try with this change if you can. Do let mew know if it solves
> your problem.
>
> This code is in function: md_get_subvol_stripe in <xf_progs>/libdisk/md.c
>
>
> /* Deduct a disk from stripe width on RAID4/5 */
> if (md.level == 4 || md.level == 5)
> md.nr_disks--;
>
> /* Update sizes */
> *sunit = md.chunk_size >> 9;
> *swidth = *sunit * md.nr_disks;
>
> return 1;
> }
>
> Regards,
> Shailendra
> Steve Cousins wrote:
>
>> 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
>>>>>
>>>>>
>>>>>
>>>>
>>
>>
>>
>
>