[mythtv-users] Slighty OT: Software raid mdadm online capacity expansion (OCE) success

[Gene Stapp]

Steven Adeff wrote:
> On 10/14/06, Gene Stapp <genestapp at gmail.com> wrote:
>   
>> Just thought I'd let everyone know I was able to do a raid 5 disk
>> expansion in mdadm software raid with no ill effects. I used mdadm 2.5.4
>> (built from source) and supposedly it is pretty safe. Following this
>> page as a guide and it worked perfectly. Took about 6 hours to reshape
>> the array. From 300gb x 4 raid 5 to 300gb x 5 raid 5. No lvm just an md0
>> mdadm device and I was still able to make 2 simultaneous HD recordings
>> and watch an HD recording while this was going on.
>>
>> page used as guide:
>> http://scotgate.org/?p=107#comments
>>
>> for me the process was:
>> |mdadm --add /dev/md0 /dev/sde1|
>>
>> then:
>> |mdadm --grow /dev/md0 --raid-devices=5
>>
>> |to find details about your raid reshaping status use:
>> cat /proc/mdstat
>>
>> to speed up reshaping use (fill in whatever speed you want where the
>> 100000 is. Default is 10000 :
>> echo -n 100000 > /proc/sys/dev/raid/speed_limit_max
>>
>> The only difference for xfs is to use the:
>>  xfs_growfs (path to mounted raid filesystem)
>>
>> Hope this is helpful as I didn't see anything in the archives on this topic,
>> Gene
>>     
>
> great to hear. I've been looking at building a RAID5 array in two
> parts (to spread out the costs), one of the things I was looking for
> was information on how long the process takes.
>
> Any idea what the speed_limit_max does?
>
>   
The speed_limit_max entry there controls how fast the raid array 
rebuilds (how much of the array's bandwidth is available to the rebuild 
process).  Make that bandwidth number higher and it goes faster but uses 
more of the throughput of the hard drives (leaving less available to say 
Myth recording on the degraded array). Using the info I posted earlier 
while you are waiting for the reshaping to finish, the array is in a 
degraded state.

Gene