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

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

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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