Re: 2x6 or 3x4 raid10 arrays ?

[Nat Makarevitch <nat@makarevitch.org>]

Keld Jørn Simonsen <keld <at> dkuug.dk> writes:

> I have understood chunk to be a set of sectors on a single device.

You are right, I completely botched my reply

>> Creating more than one array may be OK when you very
>> precisely know your load profile per table

>> your best bet is "to maintain, for each
>> request, as much disk heads available as possible", carpet-bomb the array
>> with all requests and let the elevator(s) optimize

> This is for bigger operations. I believe that for smaller operations,
> such as a random read in a database, you would only like to have one IO
> operation on one device.

We agree on this. My reply was tailored upon the prerequisite of a chunk size
defined to be slightly superior to the size of the data needed for most requests.

Using multiple arrays may be useful if all tables are accessed at similar rates
while some have much bigger average amount of bytes implied by any request:
their array need a bigger chunk size.

> > > Some other factors may be more important: such as the ability to survive
> > > disk crashes
> > 
> > That's very true, however one may not neglect logistics.

> Yes, rebuild time would also be a factor.

I think so

> Smaller raids are quicker to rebuild

It depends on device performance (putting online a recent small-capacity device
will lead to quick rebuild), workload during rebuild...

> for raid10,f2 -
> probebly limited by the write speed of the replacing device.

I think so.


--
To unsubscribe from this list: send the line "unsubscribe linux-raid" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html