[Lustre-discuss] Upgrading our filesystem

[Andreas Dilger]

On 2010-04-12, at 15:11, Norberto Meijome wrote:
> On 12 April 2010 10:15, Andreas Dilger <andreas.dilger at oracle.com>  
> wrote:
>> I would suggest to keep the OST size uniform that you migrate the
>> existing OSTs to the new 600GB drive LUNs then combine pairs of (now
>> unused) 300GB LUNs into double-sized OSTs to match the new ones.
>>
>> While the MDS will handle different-sized OSTs OK, it isn't the ideal
>> situation.
>
> Andreas,
> could you please explain ( or point to information about) why it's  
> better / ideal to have same-sized OSTs?


It boils down to the fact that if there is uneven utilization of any  
resource in the system, then performance is being wasted to some  
extent.  If we have to skip allocating objects on the smaller OSTs at  
some point (either pre-emptively because they are getting more full  
than the larger OSTs and we want to avoid over filling them, or  
because they have gotten full and we can no longer use them at all),  
then the OSS bandwidth will be underused at that time.

That said, if you are not depending on the full bandwidth of all the  
OSTs all the time, then this may be OK.

Cheers, Andreas
--
Andreas Dilger
Principal Engineer, Lustre Group
Oracle Corporation Canada Inc.