Re: 4-disk raid5 with 2 disks going bad: best way to proceed?

[Roberto Spadim <roberto@spadim.com.br>]

i'm not a master expert with linux raid, but... stop array, add 2 new
disks and make a backup (dd) of two bad disks, start array with the
new disks (must be same size)
(i don't know if raid5 have spare disks and how they work, maybe
there's a 'online' solution without stopping array)
maybe others guys here could help you better, but this one works :)

2011/4/6 rob pfile <rpfile@gmail.com>:
> Hi all,
>
> any collective wisdom on what to do here? i've got a 4-disk raid5, and the most recent checkarray showed several bad blocks caused by uncorrectable read errors on two of the disks in the array. both disks in question show 0 reallocated sectors, but one looks like this:
>
> 197 Current_Pending_Sector  0x0032   200   200   000    Old_age   Always       -       0
> 198 Offline_Uncorrectable   0x0030   200   200   000    Old_age   Offline      -       16
> 199 UDMA_CRC_Error_Count    0x0032   200   200   000    Old_age   Always       -       0
> 200 Multi_Zone_Error_Rate   0x0008   200   200   000    Old_age   Offline      -       16
>
> and the other like this:
>
> 197 Current_Pending_Sector  0x0032   200   200   000    Old_age   Always       -       14
> 198 Offline_Uncorrectable   0x0030   200   200   000    Old_age   Offline      -       3
> 199 UDMA_CRC_Error_Count    0x0032   200   200   000    Old_age   Always       -       0
> 200 Multi_Zone_Error_Rate   0x0008   200   200   000    Old_age   Offline      -       11
>
> i'm a bit worried about failing one of these disks for fear that the other might give uncorrectable read errors during the rebuild. if i *had* to choose one, should i choose the one with all the pending sectors, or the one with all the uncorrectable sectors?
>
> does it makes sense to do a smartctl -t offline scan on one or both of these disks first?
>
> i guess i could take the array offline, clone one of the disks with dd, and then swap the clone in. but... is there a way to clone one disk in the array using mdadm? in other words, is there a way to construct a clean copy of one of the disks even if there are raid-correctable read errors?
>
> i do have backups, so perhaps it will not kill me if the array dies, but i'd like to tread carefully and try and get out of this mess without nuking everything.
>
> thanks for any advice,
>
> rob
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-- 
Roberto Spadim
Spadim Technology / SPAEmpresarial
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