Re: Swap initialised as an md?

[Bill Davidsen]

Michael Tokarev wrote:

Bill Davidsen wrote:
[]
  

If you use RAID0 on an array it will be faster (usually) than just
partitions, but any process with swapped pages will crash if you lose
either drive. With RAID1 operation will be more reliable but no faster.
If you use RAID10 the array will be faster and more reliable, but most
recovery CDs don't know about RAID10 swap. Any reliable swap will also
have the array size smaller than the sum of the partitions (you knew that).



You seems to forgot to mention 2 more things:

 o swap isn't usually needed for recovery CDs
  
That's system dependent, but at least two report problems with swap if 
configured as RAID10. Confusing error messages are not a plus when you 
get to the stage of using a recovery CD. The need for swap depends on 
configuration.

 o kernel vm subsystem already can do equivalent of raid0 for swap internally,
   by means of allocating several block devices for swap space with the
   same priority.

If reliability (of swapped processes) is important, one can create several
RAID1 arrays and "raid0 them" using regular vm techniques.  The result will
be RAID10 for swap.


Sorry, no. It will be RAID0+1, not the same thing. See RAID10 description.

--
bill davidsen <[EMAIL PROTECTED]>
 CTO TMR Associates, Inc
 Doing interesting things with small computers since 1979

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Re: XFS sunit/swidth for raid10

[dean gaudet]

On Fri, 23 Mar 2007, Peter Rabbitson wrote:

> dean gaudet wrote:
> > On Thu, 22 Mar 2007, Peter Rabbitson wrote:
> > 
> > > dean gaudet wrote:
> > > > On Thu, 22 Mar 2007, Peter Rabbitson wrote:
> > > > 
> > > > > Hi,
> > > > > How does one determine the XFS sunit and swidth sizes for a software
> > > > > raid10
> > > > > with 3 copies?
> > > > mkfs.xfs uses the GET_ARRAY_INFO ioctl to get the data it needs from
> > > > software raid and select an appropriate sunit/swidth...
> > > > 
> > > > although i'm not sure i agree entirely with its choice for raid10:
> > > So do I, especially as it makes no checks for the amount of copies (3 in
> > > my
> > > case, not 2).
> > > 
> > > > it probably doesn't matter.
> > > This was essentially my question. For an array -pf3 -c1024 I get swidth =
> > > 4 *
> > > sunit = 4MiB. Is it about right and does it matter at all?
> > 
> > how many drives?
> > 
> 
> Sorry. 4 drives, 3 far copies (so any 2 drives can fail), 1M chunk.

my mind continues to be blown by linux raid10.

so that's like raid1 on 4 disks except the copies are offset by 1/4th of 
the disk?

i think swidth = 4*sunit is the right config then -- 'cause a read of 4MiB 
will stride all 4 disks...

-dean
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addingdrive to raid 1

[Robert Stanford]

Hi All, Long time Linux software raid user, first real problem.

I built md2 with 1 missing drive and am now trying to add a drive (hda4)

The partition that is hda4 was previously part of another  raid array 
md1 that no longer exists.


I have zeroed the superblock in hda4, however when I try to add it it 
sync's instantly, no rebuild.


The original raid array md1 is several years old and was built with the 
old raidtools package.


I even ran
dd if=/dev/zero of=/dev/hda4
just to be sure that nothing was left on the partition from the previous 
raid setup and still no joy.


Any help would be appreciated

Kind Regards
Robert Stanford

-
/proc/mdstat
Personalities : [raid1]
md2 : active raid1 hdc4[0]
 72894848 blocks [2/1] [U_]



mdadm --examine /dev/hdc4
/dev/hdc4:
 Magic : a92b4efc
   Version : 00.90.03
  UUID : 90844a43:c57dd8a1:5a5eed64:48faee6c
 Creation Time : Sat Mar 24 06:33:03 2007
Raid Level : raid1
  Raid Devices : 2
 Total Devices : 1
Preferred Minor : 2

   Update Time : Sun Mar 25 16:30:59 2007
 State : clean
Active Devices : 1
Working Devices : 1
Failed Devices : 1
 Spare Devices : 0
  Checksum : 32ea145b - correct
Events : 0.5610


 Number   Major   Minor   RaidDevice State
this 0  2240  active sync   /dev/hdc4

  0 0  2240  active sync   /dev/hdc4
  1 1   001  faulty removed



mdadm --examine /dev/hda4
mdadm: No super block found on /dev/hda4 (Expected magic a92b4efc, got 
)




mdadm --add /dev/md2 /dev/hda4
mdadm: hot added /dev/hda4



Personalities : [raid1]
md2 : active raid1 hda4[1] hdc4[0]
 72894848 blocks [2/2] [UU]



/var/log/kern.log
Mar 25 16:33:11 server kernel: md: bind
Mar 25 16:33:11 server kernel: RAID1 conf printout:
Mar 25 16:33:11 server kernel:  --- wd:1 rd:2
Mar 25 16:33:11 server kernel:  disk 0, wo:0, o:1, dev:hdc4
Mar 25 16:33:11 server kernel:  disk 1, wo:1, o:1, dev:hda4
Mar 25 16:33:11 server kernel: md: syncing RAID array md2
Mar 25 16:33:11 server kernel: md: minimum _guaranteed_ reconstruction 
speed: 1000 KB/sec/disc.
Mar 25 16:33:11 server kernel: md: using maximum available idle IO 
bandwidth (but not more than 20 KB/sec) for reconstruction.
Mar 25 16:33:11 server kernel: md: using 128k window, over a total of 
72894848 blocks.

Mar 25 16:33:11 server kernel: md: md2: sync done.
Mar 25 16:33:11 server kernel: RAID1 conf printout:
Mar 25 16:33:11 server kernel:  --- wd:2 rd:2
Mar 25 16:33:11 server kernel:  disk 0, wo:0, o:1, dev:hdc4
Mar 25 16:33:11 server kernel:  disk 1, wo:0, o:1, dev:hda4



mdadm --set-faulty  /dev/md2 /dev/hda4
mdadm: set /dev/hda4 faulty in /dev/md2
mdadm -r  /dev/md2 /dev/hda4
mdadm: hot removed /dev/hda4
mdadm --zero-superblock /dev/hda4



/var/log/kern.log
Mar 25 16:34:09 server kernel: raid1: Disk failure on hda4, disabling 
device.

Mar 25 16:34:09 server kernel: ^IOperation continuing on 1 devices
Mar 25 16:34:09 server kernel: RAID1 conf printout:
Mar 25 16:34:09 server kernel:  --- wd:1 rd:2
Mar 25 16:34:09 server kernel:  disk 0, wo:0, o:1, dev:hdc4
Mar 25 16:34:09 server kernel:  disk 1, wo:1, o:0, dev:hda4
Mar 25 16:34:09 server kernel: RAID1 conf printout:
Mar 25 16:34:09 server kernel:  --- wd:1 rd:2
Mar 25 16:34:09 server kernel:  disk 0, wo:0, o:1, dev:hdc4
Mar 25 16:34:13 server kernel: md: unbind
Mar 25 16:34:13 server kernel: md: export_rdev(hda4)



mdadm --examine /dev/hda4
/dev/hda4:
 Magic : a92b4efc
   Version : 00.90.03
  UUID : 90844a43:c57dd8a1:5a5eed64:48faee6c
 Creation Time : Sat Mar 24 06:33:03 2007
Raid Level : raid1
  Raid Devices : 2
 Total Devices : 2
Preferred Minor : 2

   Update Time : Sun Mar 25 16:33:11 2007
 State : clean
Active Devices : 2
Working Devices : 2
Failed Devices : 0
 Spare Devices : 0
  Checksum : 32ea14e0 - correct
Events : 0.5616


 Number   Major   Minor   RaidDevice State
this 1   341  active sync   /dev/hda4

  0 0  2240  active sync   /dev/hdc4
  1 1   341  active sync   /dev/hda4


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