Help, my disk array has one dead member

[Kevin O'Gorman]

On Wed, Mar 29, 2017 at 7:54 PM, Remi Gauvin <remi at georgianit.com> wrote:

> On 17-03-27 01:16 PM, Kevin O'Gorman wrote:
>
> Fortunately, I think RAID5 is a good fit for my use-case.  Overall,
>> it's compute-intensive, not so much DB-intensive.  My requirement of
>> the database is that it be large and reliable, not so much fast.  I
>> tend to be working on a small part of the data at a time.  I have
>> compute tasks that run for days with no disk activity at all.
>>
>
> The problem with Raid 5 is not performance, (which I think is kind of
> great,,, CPU's have long since gone past the point where parity calculation
> was an issue.)
>
> It's reliability.  Generally, there are all kinds of common failures that
> can temporarily take out 2 drives, (example, say, one of your Controller's
> that has 2 drives attached fails or just locks up somehow.)
>
> the result will be the kernel marking your array as damaged and dead. You
> can force the array to rebuild, but with the huge size of modern drives,
> having to way over 24 hours see if you succeed can be stressful.
>
> So don't temp Murphy, if using Raid-5, make sure you have good up to date
> backup at all times.
>
> If you need a system that can be recovered from failure the fastest, stick
> with Raid-1
>
>
> (Having written all that, I use Raid-5 for my own storage needs.. I'm not
> against it by any means.)
>
>
> Having just built a RAID-5, I know what you mean.  It took 3 days to
finish building the parity blocks.

However, my problem is that it takes a similar amount of time to back up a
filesystem that large (when full).  I want a filesystem that has some
recoverability without weekly 3-day backups.

I'm not going to RAID-6 because I don't have a place in this machine for
another drive.  It has 7 as it stands, if you count the SATA DVD drive.  If
this experiment is really successful, perhaps I'll combine the RAID with
one of the other drives into a new RAID-6.  I didn't want to do that to
begin with because the data now on the RAID is all related to a single
project which is just entering a new phase, and only the new stuff is going
there.

-- 
Kevin O'Gorman
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