MegaRAID - changing cache policy online

Question

I would like to perform some tests with WriteThrough and WriteBack. Is it safe to change these settings on a production system? The RAID controller doesn't have a BBU so I would like to enable WriteBack just for the duration of the test (sysbench):

# ./MegaCli64 -LDInfo -L0 -a0 | grep "Current Cache Policy:"
Current Cache Policy: WriteThrough, ReadAdaptive, Direct, No Write Cache if Bad BBU

# ./MegaCli64 -LDSetProp WB -L0 -a0

Solution

I did this several times on a test server without any problems. Also, I never read any warning or something like that to not do that online. So I guess this should be safe.

As you don't have a BBU, you need this command as well:

./MegaCli64 -LDSetProp CachedBadBBU -L0 -a0

Change back with:

./MegaCli64 -LDSetProp NoCachedBadBBU -L0 -a0

Comments

[Jeremy]

tlo's CachedBadBBU/NoCachedBadBBU settings are backwards -- You want NoCachedBadBBU if you don't have a battery backup unit. "No Write Cache if Bad BBU"

[Evan R.]

Jeremy is wrong. If you use "noCachedBadBBU", it goes back to "write through" . I just tested this. tlo is correct