Jeff V. Merkey wrote:Max Waterman wrote:
One further question. I get these messages 'in' dmesg :
sda: asking for cache data failed
sda: assuming drive cache: write through
How can I force it to be 'write back'?
Forcing write back is a very bad idea unless you have a battery backed up RAID controller.
This is not what these messages are referring to. Those write through vs. write back messages are referring to detecting the drive write cache mode, not setting it. Whether or not the write cache is enabled is used to determine whether the sd driver uses SYNCHRONIZE CACHE commands to flush the write cache on the device. If the drive says its write cache is off or doesn't support determining the cache status, the kernel will not issue SYNCHRONIZE CACHE commands. This may be a bad thing if the device is really using write caching..