Re: Need to remove failed disk from RAID5 array

[Alex <mysqlstudent@xxxxxxxxx>]

Hi,

>> That's a good argument for not using "whole disk" array members, a partition can
>> be started at a good offset and may perform better. As for the speed, since it
>> is reconstructing the array data (hope the other drives are okay), every block
>> written requires three blocks read and a reconstruct in cpu and memory. You can
>> use "blockdev" to increase readahead, and set the devices to use the deadline
>> scheduler, that _may_ improve things somewhat, but you have to read three block
>> to write one, so it's not going to be fast.
>>
>
> Read-ahead has absolutely no effect in this context.
>
> Read-ahead is a function of the page cache.  When filling the page cache,
> read-ahead suggests how much more to be read than has been asked for.
>
> resync/recovery does not use the page cache, consequently the readahead
> setting is irrelevant.
>
> IO scheduler choice may make a difference.

It's already set for cfq. I assume that would be the preferred over deadline?

I set it on the actual disk devices. Should I also set it on md0/1
devices as well? It is currently 'none'.

/sys/devices/virtual/block/md0/queue/scheduler

Thanks,
Alex
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