The write speed on the array is extremely slow
Symptom
The write speed on the 3ware RAID array is extremely slow. It also takes a very long time (many hours) to create a filesystem.
Solution
Poor write performance can occur if the controller write cache is disabled.
The write cache can be enabled using tw_cli or the 3dm2 Web interface. Here is a sample session under tw_cli:
# tw_cli info c0 Unit UnitType Status %RCmpl %V/I/M Stripe Size(GB) Cache AVrfy ------------------------------------------------------------------------------ u0 SINGLE OK - - - 232.82 OFF OFF u1 RAID-5 OK - - 64K 4190.89 OFF OFF
# tw_cli //asl44> /c0/u0 set cache=on //asl44> /c0/u1 set cache=on //asl44> info c0 Unit UnitType Status %RCmpl %V/I/M Stripe Size(GB) Cache AVrfy ------------------------------------------------------------------------------ u0 SINGLE OK - - - 232.82 ON OFF u1 RAID-5 OK - - 64K 4190.89 ON OFF
If the controller is equipped with a battery backup unit (BBU), then the write cache will be disabled if the battery has failed:
# tw_cli info c0 Unit UnitType Status %Cmpl Stripe Size(GB) Cache AVerify IgnECC ------------------------------------------------------------------------------ u0 SINGLE OK - - 465.651 OFF OFF - u1 SPARE OK - - 465.753 - OFF - u2 RAID-5 OK - 256K 1862.61 OFF OFF OFF Port Status Unit Size Blocks Serial --------------------------------------------------------------- p0 OK u0 465.76 GB 976773168 3PM06DVB p1 OK u1 465.76 GB 976773168 3PM05Z0A p2 OK u2 465.76 GB 976773168 3PM02GEB p3 OK u2 465.76 GB 976773168 3PM080NK p4 OK u2 465.76 GB 976773168 3PM0H5GQ p5 OK u2 465.76 GB 976773168 3PM0H5QT p6 OK u2 465.76 GB 976773168 3PM03139 p7 NOT-PRESENT - - - - p8 NOT-PRESENT - - - - p9 NOT-PRESENT - - - - p10 NOT-PRESENT - - - - p11 NOT-PRESENT - - - - Name OnlineState BBUReady Status Volt Temp Hours LastCapTest --------------------------------------------------------------------------- bbu On No Failed OK OK 207 10-Jul-2009
In this case, replacing the battery will re-enable the cache. After the battery has been replaced, a capacity test should be performed:
# tw_cli /c0/bbu test
According to 3ware, the battery pack should last one to two years depending on usage. It is recommended that a capacity test be performed at least every 6 months. Once the capacity has dropped below 120 hours, then the test should be performed once a month.
The write cache can be re-enabled before replacing the battery by first disabling the BBU:
# tw_cli /c0/bbu disable # tw_cli /c0/u0 set cache=on
However if the system loses power then any data still in the cache will be lost. This can result in corruption.
Battery Replacement
To replace the battery on the 9550SX BBU, please refer to page 36.
http://www.3ware.com/support/UserDocs/3ware9550SXInstallGuide.pdf
To replace the battery on the 9590SE BBU, please refer to page 33
http://www.3ware.com/support/UserDocs/3ware9590SEInstallGuide.pdf
To replace the battery on the 9650SE BBU, please refer to page 33
http://www.3ware.com/support/UserDocs/InstallGuide9650-9.5.2.pdf
To replace the battery on the 9690SA BBU, please refer to this document.
http://www.3ware.com/support/UserDocs/BBU_Remote_Battery_Install_Guide720-0171-00revA.pdf