Re-enabling a pesky write cache

So at work we have a number of disk systems made by IBM. One of them is a DS3400 filled to the brim with 1TB drives. It’s used in our backup system as a storage device. It sits idle most of the day, but is very busy at night when all of the backup schedules kick off on our various servers.

This disk system recently notified us that its cache batteries needed to be replaced. We received the batteries earlier today, and swapped them out before lunch. This was very straightforward and my co-worker and I encountered no surprises, which is always a good thing when you’re pulling controllers out of disk systems.

The only hiccup was that the write cache on the disk system would not re-enable itself. As you can see in the screen shot, it shows a status of “currently suspended.” No fun, especially as this has a negative impact on performance.

I ran a number of commands via the disk system’s CLI that I had in my notes and some I found via internet searching. None of them left me with an enabled write cache. So it was time to contact IBM. They got back to me and wanted me to try these commands:

set allLogicalDrives writeCacheEnabled=false;
set allLogicalDrives readCacheEnabled=false;
set alllogicaldrives mirrorcacheenabled=false;

to be followed by these commands:

set allLogicalDrives writeCacheEnabled=true;
set allLogicalDrives readCacheEnabled=true;
set alllogicaldrives mirrorcacheenabled=true;

I ran both sets of commands, the first set changes the cache settings to false or off.

After the second set of commands ran, I checked the logical drive in the DS3400’s profile.

Success!

Thank you IBM support for you quick response and for providing just what we needed to get the write cache enabled.