[gpfsug-discuss] Blocksize

[Alex Chekholko]

On 09/27/2016 10:02 AM, Buterbaugh, Kevin L wrote:
> 1) Let’s assume that our overarching goal in configuring the block size
> for metadata is performance from the user perspective … i.e. how fast is
> an “ls -l” on my directory?  Space savings aren’t important, and how
> long policy scans or other “administrative” type tasks take is not
> nearly as important as that directory listing.  Does that change the
> recommended metadata block size?

You need to put your metadata on SSDs.  Make your SSDs the only members 
in your 'system' pool and put your other devices into another pool, and 
make that pool 'dataOnly'.  If your SSDs are large enough to also hold 
some data, that's great; I typically do a migration policy to copy files 
smaller than filesystem block size (or definitely smaller than sub-block 
size) to the SSDs.  Also, files smaller than 4k will usually fit into 
the inode (if you are using the 4k inode size).

I have a system where the SSDs are regularly doing 6-7k IOPS for 
metadata stuff.  If those same 7k IOPS were spread out over the slow 
data LUNs... which only have like 100 IOPS per 8+2P LUN...  I'd be 
consuming 700 disks just for metadata IOPS.

-- 
Alex Chekholko chekh at stanford.edu