Re: 3-drive RAID1 for my low use home server?

[Mark Knecht <markknecht@gmail.com>]

On Wed, Mar 24, 2010 at 7:49 AM, Eric Shubert <ejs@shubes.net> wrote:
> Mark Knecht wrote:
>>
>> Hi,
>>   Just triple checking what I think I've learned here before I start
>> loading Gentoo. Parts are arriving and I'm staring to put them
>> together to build a combo low-use server (backups and MythTV) as well
>> as desktop for my wife. I can do anything up to 6 drives but want the
>> RAID to survive in the face of possibly two drive failure. This is all
>> low bandwidth stuff.
>>
>>   I'm fairly focused at this point on doing RAID1 using 3 drives.
>> Unless I hear differently I believe a 3-drive RAID1 could survive 2
>> drive failures, and as well any single drive could be taken to another
>> machine or even placed in an external USB/eSATA drive container in the
>> event of some major motherboard failure. Is any of that incorrect?
>
> All sounds right to me. Just be sure that the array is defined with 3 drives
> and no spares.
>
>>   Also, along the way folks have mentioned hot spares but I'm not
>> seeing that a hot spare does much for RAID1. Am I incorrect about
>> that?
>
> Right. The only thing it would buy you is a little write performance, but
> you'd lose a little read performance, and take a performance hit if/when one
> drive goes off.
>
>> Granted, I guess the rebuild starts automatically and maybe
>> that's worth it, but I'm thinking that mdadm can probably let me know
>> fairly quickly that I need to do some work. I've purchased 6 drives so
>> I'll have 2 or 3 spares around and I can do a hot spare but I don't
>> see the value in spinning the drive for a year burning power and
>> wearing the drive out vs. just putting it on the shelf and keeping it
>> in reserve for a rainy day.
>
> Just one thought here. There is a certain "infant mortality syndrome" that
> drives experience (according to google study). I would rotate drives from
> the shelf into service after a year or so, while they're still under
> warranty (assuming 3yr warranty). If the warranty period is less than 2yr,
> rotate them sooner.
>
> NJoy!
>
> --
> -Eric 'shubes'

Thanks Eric. I'll keep this in mind.

Other than the work involved in fixing things this is a home setup so
if it was down for a day or two it's not like a mission critical or
anything.

Also, the really critical coming from another machine that has two RAID's in it:

1) Main RAID is RAID0 using RAID class drives. (Lower reliability but
speed where I need it.)

2) Backup RAID in first machine is a 3 drive RAID 1.

3) This 2nd machine which also has RAID1 as we've been speaking aobut.

So, machine 1 runs RAID0 for work and then automatically backs up data
every few hours to a RAID1 internal to the same box. Once a day I will
then back up the machine 1 RAID1 to machine 2's RAID1 so I'm covered
twice. If one RAID1 does down then I can basically just fix it will
the other RAID1 keeps me safe.

Certainly, every so often I go offsite for even more protection.

Cheers,
Mark

Cheers,
Mark
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