On 5/12/2010 8:25 AM, Sorin Srbu wrote:
>
>> Something less than a dozen is a small number.  With 3, every write is
> going to
>> require every disk head to seek and you'll wait until the slowest one
> completes
>> before the next operation.
>
> We seem to be on different scales here. ;-) My biggest array is a six-disk
> Dell PE...

The point is simply that disk seeks are orders of magnitude slower than 
any other computer operation so you don't get any speed until the heads 
in the array start working mostly independently and have better odds of 
already being near the right place.  With raid5 that takes a lot of drives.

> So a small number of drives, having a nearly completely filled pool, huge
> backups that go well into the blackout-period (when I  might want to check
> and possibly restore stuff) and plenty of small files all spells (more or
> less) slowness and potential disaster then?

The other thing that can help is available RAM to act as a filesystem 
buffer since it can eliminate many seeks you might need for reads.

-- 
   Les Mikesell
    lesmikesell AT gmail DOT com


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