Disk writes extremely slow on SATA RAID

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Posted by getweb, 01-10-2008, 08:14 PM
I'm running into a problem with a relatively new (2 months old) server. I have just a few accounts on it, and I'm already noticing unusual loads, for the... load. After some benchmarking with bonnie++ (and plain old "dd") there is clearly a problem. Isn't a write-speed over 7MB/s reasonable to expect? Also look at the low CPU times... Anyway running the same test on a similar but older AND busier server showed much better results than this. In fact dd'ing a 1GB file from /dev/zero "finished" in about 10 seconds but then pegged the server at 99% iowait (wa) for a full three minutes (until done being written from cache I assume), bringing load to 15.00 That's all the info I have so far... the data center just replaced the card (which gave no errors) with no effect. Running these benchmark tests is about the extend of my hardware experience. Thanks in advance for any advice/leads to follow.
Posted by getweb, 01-10-2008, 08:23 PM
Sorry - I suppose I do know more stuff. This is a Dell PowerEdge 840 with "3ware Inc 9550SX SATA-RAID" card, with driver 3w_9xxx. Connected is two WD 250GB/7200RPM SATA drives in a mirrored pair configuration. 2.4GHz Xeon 3060 with 1067FSB MBoard.
Posted by layer0, 01-10-2008, 09:49 PM
Is write cache enabled?
Posted by getweb, 01-10-2008, 10:05 PM
Wait... so you're telling me: just fixed my server? Stuff already seems to be running better. I didn't even know "sdparm" or "wce" existed until 10 minutes ago; hopefully this helps someone else. BUT - now why is that off by default, are there risks? (ie Power Failure, etc?) EDIT: ...kinda dramatic. In fact I'm going to re-run with a bigger sample, is a terabyte/sec really possible? Or just unimagineable? Last edited by getweb; 01-10-2008 at 10:13 PM. Reason: Add results table
Posted by wKkaY, 01-11-2008, 09:07 AM
Can you post the output of: tw_cli /c0 show all
Posted by getweb, 01-11-2008, 10:03 AM
Server is running significantly better... I mean it seems like a no-brainer, but odd it was off in the first place. Avg load has fallen from 0.80+ to under 0.10. Here's the output: /c0 Driver Version = 2.26.05.007 /c0 Model = 9550SX-4LP /c0 Available Memory = 112MB /c0 Firmware Version = FE9X 3.04.00.005 /c0 Bios Version = BE9X 3.04.00.002 /c0 Boot Loader Version = BL9X 3.02.00.001 /c0 Serial Number = L020909B7121156 /c0 PCB Version = Rev 032 /c0 PCHIP Version = 1.60 /c0 ACHIP Version = 1.70 /c0 Number of Ports = 4 /c0 Number of Drives = 2 /c0 Number of Units = 1 /c0 Total Optimal Units = 1 /c0 Not Optimal Units = 0 /c0 JBOD Export Policy = off /c0 Disk Spinup Policy = 1 /c0 Spinup Stagger Time Policy (sec) = 2 /c0 Auto-Carving Policy = off /c0 Auto-Carving Size = 2048 GB /c0 Auto-Rebuild Policy = on /c0 Controller Bus Type = PCIX /c0 Controller Bus Width = 64 bits /c0 Controller Bus Speed = 133 Mhz Unit UnitType Status %RCmpl %V/I/M Stripe Size(GB) Cache AVrfy ------------------------------------------------------------------------------ u0 RAID-1 OK - - - 232.82 ON OFF Port Status Unit Size Blocks Serial --------------------------------------------------------------- p0 OK u0 232.83 GB 488281250 WD-WCANK7710148 p1 OK u0 232.83 GB 488281250 WD-WCANK7716042 p2 NOT-PRESENT - - - - p3 NOT-PRESENT - - - -
Posted by HoundOfTheSmith, 01-11-2008, 10:29 AM
If you have a battery backup unit try issuing the following from the tw_cli command: /c0/u0 set storsave=perform You can find out the current setting with "/c0/u0 show storsave"
Posted by getweb, 01-11-2008, 11:08 AM
Thanks, Hound. On your tip I found the user guide and read about it. I do not appear to have a BBU (I'm checking with DC to confirm) and I have some room to work with, so I might go with "balanced" or back to "protect" for now. That said, I'm running "perform" today just for comparison. I might do another benchmark when things are quiet. Thanks for all the help. I'm considering this "Resolved" but still welcome suggestions.
Posted by Bilco105, 01-11-2008, 11:18 AM
Writecaching is disabled by default on raid devices which do not have a BBU connected. You can enable it, but I wouldn't reccommend it. Writecaching is just that, if you enable it without a BBU connected, you risk dataloss.