alternate (RAID1) install

[Rashkae]

On 02/28/2012 09:26 AM, Liam Proven wrote:
> On 28 February 2012 01:41, Rashkae<ubuntu at tigershaunt.com>  wrote:
>> On 02/27/2012 07:47 PM, Liam Proven wrote:
>>> Note that you can't, AFAIK, mirror swap partitions, but you wouldn't
>>> want to. Just make 2 × half-size swap partitions: so if you want 4GB
>>> swap, make 2 × 2GB partitions. The kernel will use two, no problem.
>> I'll have to respectfully disagree.
>>
>> 1. You can, in fact, mirror swap partitions, (or any other form of raid.)
>>   Just use the md device as your swap.
>>
>> 2.  The purpose of raid is not backup, it's reliability.  You want the
>> computer to keep running and automagically recover from hard drive failures.
>>   If you're swap is not on a raid and a hard drive hiccups, the OS will
>> crash.
> Hmmm. All right, I see what you mean. It would damage performance,
> though, I think.
>

Yes and no.  A raid array should have very little impart on the 
performance (vs. a single drive.)  It's true that your suggestion, if 
implemented well, would double the theoretical Swap performance.  (If 
you tweak the priority of swap partitions in the fstab so they are both 
the same, Linux will spread the load evenly between the two discs.).

However...

Just like the infamous Raid 0, splitting swap between two discs 
literally doubles the odds that the server will come to screaming halt 
in the middle of the work day due to some hard drive error.

On a reasonably well tuned system, Swap should almost only be used to 
quietly swap out (and sometimes in) rarely used bits of memory in the 
background.  If your page file is being hit so hard that performance if 
even an issue, you have another problem that needs fixing with either 
$20 of memory and/or some adjustment of the 'swapinness' knob.