[gpfsug-discuss] Flash for metadata

[Simon Thompson (Research Computing - IT Services)]

Hi Paul,

Thanks, interestingly the FS-900 only does raid5. I get no choice about that, I do get a sector size choice when I create a lun on it...

I was also wondering how gpfs would do a metadata update. Would it be smart enough to know the sector size was 512b and only modify that, or would it always do a read modify write on the whole 4k inode?

Simon

-----Original Message-----
From: Sanchez, Paul [Paul.Sanchez at deshaw.com<mailto:Paul.Sanchez at deshaw.com>]
Sent: Monday, May 16, 2016 10:28 AM GMT Standard Time
To: gpfsug-discuss at spectrumscale.org
Subject: Re: [gpfsug-discuss] Flash for metadata

Simon,

I can’t speak specifically to the FS-900, since I generally use Dell Compellent and NetApp EF arrays for flash today.  But I also take care to ensure that the system pool metadata NSDs use RAID10 (or equivalent) rather than RAID5/6.  For small 4K metadata writes, on a 4K blocksize LUN this could result in optimal writes.  For larger native blocksize LUNs, it eliminates the parity calculation for read-modify-write operations.

Thanks,
Paul

From: gpfsug-discuss-bounces at spectrumscale.org [mailto:gpfsug-discuss-bounces at spectrumscale.org] On Behalf Of Simon Thompson (Research Computing - IT Services)
Sent: Monday, May 16, 2016 9:44 AM
To: gpfsug-discuss at spectrumscale.org
Subject: [gpfsug-discuss] Flash for metadata

Hi all

I'm currently about to deploy some flash systems (FS-900) to take our metadata for one of our Spectrum Scale file-systems. We use 4k inodes for this file-system.

On the FS-900, when creating a volume, we get a choice of 512b or 4k sectors. Does anyone have a suggestion on this? On a spinning disk RAID array, I get what a strip size is and we'd use multiples of the stripe where possible for the block size.

Is the sector size on the FS-900 the smallest chunk that can be written out? And so would it make sense to use 4k sectors for 4k GPFS inodes right?

Related. In the deployment guide for the FS-900 arrays, if one is using a file-system (e.g. XFS) on the array the guide talks about aligning the partitions with with array, when GPFS is used on a storage array, does it automatically work out the sector alignment?


Thanks

Simon
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