'hdparm -W 0'

Posted May 24, 2008 20:13 UTC (Sat) by giraffedata (guest, #1954)
In reply to: 'hdparm -W 0' by tarvin
Parent article: Barriers and journaling filesystems

To be precise: ordering of write commands, ordering of hardening to disk, and write caching (in the drive) are all separate things. With write caching turned off, the drive can still reorder the write commands and write the data to the platters in random order. But Linux will always know when the data has hit the platter and won't initiate the commit record until the journal data it covers is on the platter.

Linux can have multiple writes in progress at the disk drive (sent to the drive but the drive hasn't responded) at the same time, independent of write caching.