[gpfsug-discuss] default inode size

[Aaron Knister]

I'm not sure because I've not tried it but if you chose an inode size 
less than 4K does the FS still show as being 4K aligned? If it doesn't 
this could prevent you from expanding the metadata capacity of the FS in 
the future because in a non 4k aligned fs GPFS won't let you add 4K 
sector size LUNS that contain metadata.

-Aaron

On 3/15/17 9:46 AM, Lukas Hejtmanek wrote:
> On Wed, Mar 15, 2017 at 09:36:24AM -0400, Stephen Ulmer wrote:
>> What’s the average file size? Every file that is less than *about* 3.5K will wind up in the (4k) inode itself.
>
> average file size is about 4MB.
>
>> Also check the HW sector size of the SSDs (many are 4K now). If that’s the case, you’ll actually be much more efficient from an access point of view with 4K inodes.
>
> HW sector size reported by disk array is 512B. SSD itself uses 4k though,
> however, Linux thinks it is only 512B.
>
>> If you don’ t have 1PB of data yet (or won’t in the next year or so), you can always expand the system pool with more SSDs in the future.
>
> I cannot. I don't have free HW slots.
>
>> It’s not scary to pick another size — it works just fine, but you’re about to create a filesystem that will be a pain in the rear to change. It will take a long time to move/backfill even a few hundred TB of data if you change you mind later. You’ll definitely give up (possibly future) features by choosing not 4K, but you’ve got the flexibility to do so. :)
>
> But at least I will have space to store metadata :)
>

-- 
Aaron Knister
NASA Center for Climate Simulation (Code 606.2)
Goddard Space Flight Center
(301) 286-2776