PE2950, LSI SAS -> SATA very slow

Adam Nielsen adam.nielsen at uq.edu.au
Mon May 3 19:32:25 CDT 2010


> 10MB/sec does seem extremely poor. we've had read slowness when Linux block
> device read-ahead was too small. Once properly configured, performance on
> RAID-5 went from 150MB/sec to 500MB/sec, so the difference is dramatic. we
> usually tune read-ahead (in Linux) buffers starting from 8MB to 32MB and
> benchmark to see what works best. but your problem may be elsewhere... we've
> never seen 10MB/sec...

Have you got any pointers to where this can be adjusted?  It seems 
(according to Google) there are countless methods and patches, most of 
which are for rather old kernel versions.

> On the PERC5/I, 8x HDD, RAID-5, we can get 400-500MB/sec sequential
> read/writes. I believe PERC5/I uses the LSISAS1068E with a Intel IOP333.

Is this with SATA disks?  I completely forgot about lspci (thanks Dan!), 
the card is:

01:00.0 SCSI storage controller: LSI Logic / Symbios Logic SAS1068E 
PCI-Express Fusion-MPT SAS (rev 08)
     Subsystem: Dell SAS 6/iR Integrated RAID Controller
     Flags: bus master, fast devsel, latency 0, IRQ 374
     I/O ports at ec00 [size=256]
     Memory at fc4fc000 (64-bit, non-prefetchable) [size=16K]
     Memory at fc4e0000 (64-bit, non-prefetchable) [size=64K]
     Expansion ROM at fc500000 [disabled] [size=1M]
     Capabilities: [50] Power Management version 2
     Capabilities: [68] Express Endpoint, MSI 00
     Capabilities: [98] Message Signalled Interrupts: Mask- 64bit+
         Count=1/1 Enable+
     Capabilities: [b0] MSI-X: Enable- Mask- TabSize=1
     Capabilities: [100] Advanced Error Reporting
         UESta:  DLP- SDES- TLP- FCP- CmpltTO- CmpltAbrt- UnxCmplt- RxOF-
             MalfTLP- ECRC- UnsupReq- ACSVoil-
         UEMsk:  DLP- SDES- TLP- FCP- CmpltTO+ CmpltAbrt+ UnxCmplt+ RxOF-
             MalfTLP- ECRC- UnsupReq+ ACSVoil-
         UESvrt: DLP+ SDES- TLP+ FCP+ CmpltTO- CmpltAbrt- UnxCmplt- RxOF+
             MalfTLP+ ECRC+ UnsupReq- ACSVoil-
         CESta:  RxErr- BadTLP- BadDLLP- Rollover- Timeout- NonFatalErr-
         CESta:  RxErr- BadTLP+ BadDLLP+ Rollover+ Timeout+ NonFatalErr-
         AERCap: First Error Pointer: 00, GenCap+ CGenEn- ChkCap+ ChkEn-
     Kernel driver in use: mptsas

With sequential reads I can get up to around 50MB/sec per disk, so maybe 
all my problems are related to issues with seeking?

Cheers,
Adam.



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