Activate the write cache on a 3ware Raid controller

Without the write cache 3ware raid contollers can be painfuly slow. To activate the write cache do the following. First find the correct number of you raid controller. And also the unit that you would like to switch the cache on for.

tw_cli /c0 show

Unit UnitType Status %RCmpl %V/I/M Stripe Size(GB) Cache AVrfy
——————————————————————————
u0 RAID-1 OK – – – 153.385 – –

Port Status Unit Size Blocks Serial
—————————————————————
p0 OK u0 153.38 GB 321672960 WD-WCANM3649095
p1 OK u0 153.38 GB 321672960 WD-WCANM3649568

The command: tw_cli /c0 show gives you an overwiew of the first controller in the system. If you have more than one controller you can use c2 c3 and so on. Now we know that we have one raid controller and also one unit we can switch on the cache for it.

tw_cli set cache c0 u0 on

This command will switch on the write cache for the first controller 0 and unit 0. If you have more than one controller or units please repeat this step. Afterwards check that the cache has been activated:

server142:~# tw_cli /c0 show

Unit UnitType Status %RCmpl %V/I/M Stripe Size(GB) Cache AVrfy
——————————————————————————
u0 RAID-1 OK – – – 153.385 W –

Port Status Unit Size Blocks Serial
—————————————————————
p0 OK u0 153.38 GB 321672960 WD-WCANM3649095
p1 OK u0 153.38 GB 321672960 WD-WCANM3649568

Notice the W next to Cache thats it you have increased your write performance. Please remember that you can lose data if you activate the write cache without a battery backup unit. On a power loss you will lose the cached data. 3ware only produces battery backup units for the larger controllers 4 port and greater which sucks.

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