[Gllug] Hard disk recommendations please

[general_email at technicalbloke.com]

On 02/12/10 17:39, Richard Jones wrote:
> On Thu, Dec 02, 2010 at 11:24:29AM +0000, Patrick Moody wrote:
>    
>> I am planning to expand the capacity of my server, which runs Ubuntu
>> 10.04 LTS.  I'd like to add a 1TB disk of the low power/green sort,
>> set up LVM on it and copy the contents of the existing(non LVM) 750GB
>> to it, before combining the 2.
>>      
> "Combining" in what way?
>
> I'm a bit worried about this plan over all, since there is no
> redundancy.  While I'm sure you regularly back up the disks it's still
> better to add some redundancy (in addition to backups) so that you
> won't have to handle a painful and lengthy restore when one of the
> disks fails.
>
> Given that, I'd buy 2 of the 1TB disks and put them together in a RAID
> 1 configuration, yielding about 1TB of usable space, with everything
> being duplicated on each disk.  Or 2 x 2TB disks if you can afford it.
>
> This leaves your old 750GB disk with nothing to do.
>
>    


Of course adding a second drive doubles both your power consumption and 
your chances of something going wrong ;) Having spent much of the last 
week troubleshooting a raid on the cheap system I'm not sure those 
"green" drives are really up to the job of being in a raid. I've 
experienced numerous sync losses/rebuilds and a lot of sector level 
corruption on the freeNas I built with these type of drive at the start 
of the year despite disabling the power saving features at the start.

The 3 non-raided caviar greens I run at home (which take a far heavier 
battering) have all behaved themselves impeccably over the years. I have 
disabled the power saving auto spindown features on these too. They run 
surprisingly fast (> 80MB/s), certainly good enough to keep up with 
domestic service on a GB LAN

On balance the raided setup has caused me WAY more pain and cost me WAY 
more time than the non-raided system with the same disks.

As for power saving these things are VERY power efficient. Generally 
they draw about 6W so, even presuming expensive (15p/KWh) electricity it 
would cost you less than a tenner a year to keep it on 24/7/365. If it 
wears out in half the time because it's forever spinning up and down I 
reckon the environmental cost of you returning it then having another 
one made and shipped back would be significantly worse than if you'd 
just used a little more electricity in the first place. Also, if your 
drives have to wake up every other time you need something on them your 
response times are going to blow and it's going to cause that little bit 
more strain on your PSU !

Roger.



>> Firstly; any comments on the viability of my plan.  Particularly any
>> advice about using LVM as it's my first time doing it it seems like it
>> should meet my needs in this case.
>>      
> LVM is great for flexibility.  In this case I'd suggest LVM on top of
> software RAID (/dev/md0).  For one thing this will allow you in future
> to live pvmove the data to another pair of disks.  Or lvextend across
> another pair of disks.
>
>    
>> Secondly; Amazon are selling a Western Digital Caviar Green 1Tb for
>> £40 inc delivery, which seems like a pretty good deal.  However I read
>> some reviews of the caviar green series suggesting their power saving
>> features aren't well suited to use in NAS boxes running Linux because
>> the heads get parked after 8 seconds out of use and are then un-parked
>> repeatedly.  This causes the drives to work themselves to an early
>> death, according to the reviewers.  Is this likely to be a problem in
>> a normal server setup as well, or is the issue more likely confined to
>> NAS boxes?
>>      
> I'd be a bit surprised if you couldn't configure this timeout using
> hdparm.
>
> Rich.
>
>    

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