Re: [gpfsug-discuss] Metadata with GNR code

Thu, 20 Sep 2018 17:35:02 -0700

Simon,
 
My recommendation is still very much to use SSD for Metadata and NL-SAS for data and
the GH14 / GH24 Building blocks certainly make this much easier.
 
Unless your filesystem is massive (Summit sized) you will typically still continue to benefit from the Random IO performance of SSD (even RI SSD) in comparison to NL-SAS.
 
It still makes more sense to me to continue to use 2 copy or 3 copy for Metadata even in ESS / GNR style environments.  The read performance for metadata using 3copy is still significantly better than any other scenario.
 
As with anything there are exceptions to the rule, but my experiences with ESS and ESS with SSD so far still maintain that the standard thoughts on managing Metadata and Small file IO remain the same -- even with the improvements around sub blocks with Scale V5.
 
MDtest is still the typical benchmark for this comparison and MDTest shows some very clear differences  even on SSD when you use a large filesystem block size with more sub blocks vs a smaller block size with 1/32 subblocks
 
This only gets worse if you change the storage media from SSD to NL-SAS
Andrew Beattie
Software Defined Storage  - IT Specialist
Phone: 614-2133-7927
 
 
----- Original message -----
From: Simon Thompson <[email protected]>
Sent by: [email protected]
To: "[email protected]" <[email protected]>
Cc:
Subject: [gpfsug-discuss] Metadata with GNR code
Date: Fri, Sep 21, 2018 3:29 AM
 

Just wondering if anyone has any strong views/recommendations with metadata when using GNR code?

 

I know in “san” based GPFS, there is a recommendation to have data and metadata split with the metadata on SSD.

 

I’ve also heard that with GNR there isn’t much difference in splitting data and metadata.

 

We’re looking at two systems and want to replicate metadata, but not data (mostly) between them, so I’m not really sure how we’d do this without having separate system pool (and then NSDs in different failure groups)….

 

If we used 8+2P vdisks for metadata only, would we still see no difference in performance compared to mixed (I guess the 8+2P is still spread over a DA so we’d get half the drives in the GNR system active…).

 

Or should we stick SSD based storage in as well for the metadata pool? (Which brings an interesting question about RAID code related to the recent discussions on mirroring vs RAID5…)

 

Thoughts welcome!

 

Simon

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