[gpfsug-discuss] RAID config for SSD's used for data
Uwe Falke
UWEFALKE at de.ibm.com
Thu Apr 20 09:11:15 BST 2017
Some thoughts:
you give typical cumulative usage values. However, a fast pool might
matter most for spikes of the traffic. Do you have spikes driving your
current system to the edge?
Then: using the SSD pool for writes is straightforward (placement), using
it for reads will only pay off if data are either pre-fetched to the pool
somehow, or read more than once before getting migrated back to the HDD
pool(s). Write traffic is less than read as you wrote.
RAID1 vs RAID6: RMW penalty of parity-based RAIDs was mentioned, which
strikes at writes smaller than the full stripe width of your RAID - what
type of write I/O do you have (or expect)? (This may also be important for
choosing the quality of SSDs, with RMW in mind you will have a comparably
huge amount of data written on the SSD devices if your I/O traffic
consists of myriads of small IOs and you organized the SSDs in a RAID5 or
RAID6)
I suppose your current system is well set to provide the required
aggregate throughput. Now, what kind of improvement do you expect? How are
the clients connected? Would they have sufficient network bandwidth to see
improvements at all?
Mit freundlichen Grüßen / Kind regards
Dr. Uwe Falke
IT Specialist
High Performance Computing Services / Integrated Technology Services /
Data Center Services
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gpfsug-discuss-bounces at spectrumscale.org wrote on 04/19/2017 09:53:42 PM:
> From: "Buterbaugh, Kevin L" <Kevin.Buterbaugh at Vanderbilt.Edu>
> To: gpfsug main discussion list <gpfsug-discuss at spectrumscale.org>
> Date: 04/19/2017 09:54 PM
> Subject: [gpfsug-discuss] RAID config for SSD's used for data
> Sent by: gpfsug-discuss-bounces at spectrumscale.org
>
> Hi All,
>
> We currently have what I believe is a fairly typical setup ?
> metadata for our GPFS filesystems is the only thing in the system
> pool and it?s on SSD, while data is on spinning disk (RAID 6 LUNs).
> Everything connected via 8 Gb FC SAN. 8 NSD servers. Roughly 1 PB
> usable space.
>
> Now lets just say that you have a little bit of money to spend.
> Your I/O demands aren?t great - in fact, they?re way on the low end
> ? typical (cumulative) usage is 200 - 600 MB/sec read, less than
> that for writes. But while GPFS has always been great and therefore
> you don?t need to Make GPFS Great Again, you do want to provide your
> users with the best possible environment.
>
> So you?re considering the purchase of a dual-controller FC storage
> array with 12 or so 1.8 TB SSD?s in it, with the idea being that
> that storage would be in its? own storage pool and that pool would
> be the default location for I/O for your main filesystem ? at least
> for smaller files. You intend to use mmapplypolicy nightly to move
> data to / from this pool and the spinning disk pools.
>
> Given all that ? would you configure those disks as 6 RAID 1 mirrors
> and have 6 different primary NSD servers or would it be feasible to
> configure one big RAID 6 LUN? I?m thinking the latter is not a good
> idea as there could only be one primary NSD server for that one LUN,
> but given that: 1) I have no experience with this, and 2) I have
> been wrong once or twice before (<grin>), I?m looking for advice.
Thanks!
>
> ?
> Kevin Buterbaugh - Senior System Administrator
> Vanderbilt University - Advanced Computing Center for Research and
Education
> Kevin.Buterbaugh at vanderbilt.edu - (615)875-9633
>
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