Extreme slow read performance with HP SSD SmartCache

[robhost]

Hi,

we've got a new HP DL180 with 2x240 GB SSD Cache (RAID1, HP SmartCache on Smart Array P840 Controller) and 10 spinning drives (RAID10).

But, when activated, pveperf is incredible slow:

CPU BOGOMIPS:      115186.44
REGEX/SECOND:      1845763
HD SIZE:           24.48 GB (/dev/mapper/pve-root)
BUFFERED READS:    24.65 MB/sec
AVERAGE SEEK TIME: 6.51 ms
FSYNCS/SECOND:     6361.91
DNS EXT:           3.20 ms
DNS INT:           3.31 ms

It seems, read in general is extreme slow:

hdparm -tT --direct /dev/sda

/dev/sda:
 Timing O_DIRECT cached reads:   890 MB in  2.00 seconds = 444.90 MB/sec
 Timing O_DIRECT disk reads: 204 MB in  3.16 seconds =  64.53 MB/sec

SSD Cache seems ok and used, but why so slow? We've tested with 2 different SSDs, both with same problems.

When disabled, we got >500MB/s from the spinning drives (RAID10 with 10 drives).
Any ideas on that?

 

[udo]

Hi,

we've got a new HP DL180 with 2x240 GB SSD Cache (RAID1, HP SmartCache on Smart Array P840 Controller) and 10 spinning drives (RAID10).

But, when activated, pveperf is incredible slow:

CPU BOGOMIPS:      115186.44
REGEX/SECOND:      1845763
HD SIZE:           24.48 GB (/dev/mapper/pve-root)
BUFFERED READS:    24.65 MB/sec
AVERAGE SEEK TIME: 6.51 ms
FSYNCS/SECOND:     6361.91
DNS EXT:           3.20 ms
DNS INT:           3.31 ms

It seems, read in general is extreme slow:

hdparm -tT --direct /dev/sda

/dev/sda:
 Timing O_DIRECT cached reads:   890 MB in  2.00 seconds = 444.90 MB/sec
 Timing O_DIRECT disk reads: 204 MB in  3.16 seconds =  64.53 MB/sec

SSD Cache seems ok and used, but why so slow? We've tested with 2 different SSDs, both with same problems.

When disabled, we got >500MB/s from the spinning drives (RAID10 with 10 drives).
Any ideas on that?

Hi,
what kind of SSDs do you use?

I assume the SSDs has problems with sync or garbage collection.
Have you tried an DC ready SSD like the Intel DC S3700?

Udo

 

[robhost]

what kind of SSDs do you use?

We use INTEL SSDSC2BW24. These are performing very well in single or other RAID setups, so whats the difference when using them as SmartCache drives?

 

[spirit]

We use INTEL SSDSC2BW24. These are performing very well in single or other RAID setups, so whats the difference when using them as SmartCache drives?

Hi, you need ssd with can do fast syncronous write.

AFAIK, intel 530 are pretty slow for this.
You need to use datacenter quality drive.

Here some benchmark for ceph journal with different ssd drives, this is exactly the same in your case.

http://www.sebastien-han.fr/blog/20...-if-your-ssd-is-suitable-as-a-journal-device/

 

[robhost]

Thanks, very helpful. We'll have a look into this and try other SSDs.

 

[robhost]

Update:

With Intel DC SSDs it works

/dev/sda:
Timing O_DIRECT cached reads: 1278 MB in 2.00 seconds = 638.74 MB/sec
Timing O_DIRECT disk reads: 2062 MB in 3.00 seconds = 687.16 MB/sec

/dev/sda:
Timing O_DIRECT cached reads: 1252 MB in 2.00 seconds = 626.05 MB/sec
Timing O_DIRECT disk reads: 2018 MB in 3.00 seconds = 672.29 MB/sec

/dev/sda:
Timing O_DIRECT cached reads: 1282 MB in 2.00 seconds = 640.87 MB/sec
Timing O_DIRECT disk reads: 2054 MB in 3.00 seconds = 684.43 MB/sec

/dev/sda:
Timing O_DIRECT cached reads: 1274 MB in 2.00 seconds = 636.22 MB/sec
Timing O_DIRECT disk reads: 2104 MB in 3.01 seconds = 697.86 MB/sec

 

[Phinitris]

Hi robhost,I'm currently encountering a similar issue.Can you tell me the exact Intel Datacenter model you are using right now?Best regardsPhinitris

 

[robhost]

Sure, we're using Intel® SSD DC S3700 Series (SSDSC2BA20) right now and it works like a charme
Details: http://ark.intel.com/products/71914/Intel-SSD-DC-S3700-Series-200GB-2_5in-SATA-6Gbs-25nm-MLC

 

[Phinitris]

Thank you

 

[mir]

If DC 3700 is to much for your budget the much cheaper DC 3510 also works great.