Re: proactive raid5 disk replacement success (using bitmap + raid1)

[Ming Zhang <mingz@ele.uri.edu>]

ic. thx for clarifying.

ming

On Thu, 2006-06-22 at 17:09 -0700, dean gaudet wrote:
> well that part is optional... i wasn't replacing the disk right away 
> anyhow -- it had just exhibited its first surface error during SMART and i 
> thought i'd try moving the data elsewhere just for the experience of it.
> 
> -dean
> 
> On Thu, 22 Jun 2006, Ming Zhang wrote:
> 
> > Hi Dean
> > 
> > Thanks a lot for sharing this.
> > 
> > I am not quite understand about these 2 commands. Why we want to add a
> > pre-failing disk back to md4?
> > 
> > mdadm --zero-superblock /dev/sde1
> > mdadm /dev/md4 -a /dev/sde1
> > 
> > Ming
> > 
> > 
> > On Sun, 2006-04-23 at 18:40 -0700, dean gaudet wrote:
> > > i had a disk in a raid5 which i wanted to clone onto the hot spare... 
> > > without going offline and without long periods without redundancy.  a few 
> > > folks have discussed using bitmaps and temporary (superblockless) raid1 
> > > mappings to do this... i'm not sure anyone has tried / reported success 
> > > though.  this is my success report.
> > > 
> > > setup info:
> > > 
> > > - kernel version 2.6.16.9 (as packaged by debian)
> > > - mdadm version 2.4.1
> > > - /dev/md4 is the raid5
> > > - /dev/sde1 is the disk in md4 i want to clone from
> > > - /dev/sdh1 is the hot spare from md4, and is the clone target
> > > - /dev/md5 is an unused md device name
> > > 
> > > here are the exact commands i issued:
> > > 
> > > mdadm -Gb internal --bitmap-chunk=1024 /dev/md4
> > > mdadm /dev/md4 -r /dev/sdh1
> > > mdadm /dev/md4 -f /dev/sde1 -r /dev/sde1
> > > mdadm --build /dev/md5 -ayes --level=1 --raid-devices=2 /dev/sde1 missing
> > > mdadm /dev/md4 --re-add /dev/md5
> > > mdadm /dev/md5 -a /dev/sdh1
> > > 
> > > ... wait a few hours for md5 resync...
> > > 
> > > mdadm /dev/md4 -f /dev/md5 -r /dev/md5
> > > mdadm --stop /dev/md5
> > > mdadm /dev/md4 --re-add /dev/sdh1
> > > mdadm --zero-superblock /dev/sde1
> > > mdadm /dev/md4 -a /dev/sde1
> > > 
> > > this sort of thing shouldn't be hard to script :)
> > > 
> > > the only times i was without full redundancy was briefly between the "-r" 
> > > and "--re-add" commands... and with bitmap support the raid5 resync for 
> > > each of those --re-adds was essentially zero.
> > > 
> > > thanks Neil (and others)!
> > > 
> > > -dean
> > > 
> > > p.s. it's absolutely necessary to use "--build" for the temporary raid1 
> > > ... if you use --create mdadm will rightfully tell you it's already a raid 
> > > component and if you --force it then you'll trash the raid5 superblock and 
> > > it won't fit into the raid5 any more...
> > > -
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> >