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writeback cache

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Doug Wogan
Regular Advisor

writeback cache

I'm looking for opinions of enabling writeback cache on a cr3500 array controller. The controller is in a CL1850 for the external array. (cluster in a box) Can it be enabled after the array has been configured? What are the adverse effects?
3 REPLIES
Leonard Davison
Frequent Advisor

Re: writeback cache

Doug
Should be able to enable it at any time with no adverse affects. In fact you should notice an increase in performance.
You may run a slight risk of data loss during a power failure because data is in cache and not on the disk yet but if your UPS is good and the battery on the controller is good, you're all set.
Martin Breidenbach
Honored Contributor
Solution

Re: writeback cache

I haven't installed a CL1850 but I've installed NetServer clusters with sharded SCSI configuration.

Is this the controller which controlles the shared disk ? One controller in each cluster node ? Both connected to the shared disk ?

In that case DONT enable write cache or you may loose or corrupt data.

Imagine this scenarion:

Node 1 controlls the shared storage.
Node 1 writes data to write cache.
A failover happens while data is still in the write cache.
Node 2 changes data on the drives (normal operation)
Failback happens.
Controller in Node 1 writes its OLD data which is still in write cache over NEW data on the hard drives.

NOT GOOD.
Leonard Davison
Frequent Advisor

Re: writeback cache

Ahhhhh....Yes, quite correct I had forgotten about the failover....DO NOT DO IT.