Turning off caching

Posted Aug 11, 2013 2:02 UTC (Sun) by giraffedata (subscriber, #1954) [Link]

So you copy the whole partition, check that there is no error writing, drop the cache, read it back and check there is no error reading, and check the checksum/SHA1 of the whole partition.

Why don't you just use O_DIRECT?

One good reason is because then you don't get all the benefits of caching. There's a good reason systems normally write through the buffer/cache, and it probably applies here: you want the kernel to be able to choose the order and size of writes to the device, independent of the order and size of writes by the application. For speed and such.

But I remember using an ioctl(BLKFLSBUF) to purge just the cache of a particular device, for speed testing; that's a lot less reckless than dropping every cached piece of information from the entire system. I wonder if that still works.