Re: swidth with mdadm and RAID6

[Shailendra Tripathi <stripathi@agami.com>]

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
>>>>>
>>>>>
>>>>>       
>>>>
>>
>>  
>>
>
>