Il 27/09/2013 10:58, Chun Yan Liu ha scritto: >> If so, you could run QEMU with "cache=unsafe" and have >> basically the same data safety guarantees as "cache=writeback" on >> every other file system. > "cache=unsafe" means it never calls fsync() ?
Yes. However, metadata writes are still done and ordered correctly with respect to data writes. > If so, it seems to be > not proper to use this option to disk image of a running VM. In case > someone has run the VM for a very long time and made many changes > already on the disk image, but all those are in cache (?) Then due to > a power off, all these changes are lost. Although the disk image is > still in a consistent data status, but the data is maybe too old. Perhaps for btrfs-cow a different strategy is better, with fsyncs coalesced and issued by QEMU every N seconds. Paolo
