Am 05.08.2020 um 04:38 hat Ying Fang geschrieben: > From: fangying <fangyi...@huawei.com> > > When qemu or qemu-nbd process uses a qcow2 image and configured with > 'cache = none', it will write to the qcow2 image with a cache to cache > L2 tables, however the process will not use L2 tables without explicitly > calling the flush command or closing the mirror flash into the disk. > Which may cause the disk data inconsistent with the written data for > a long time. If an abnormal process exit occurs here, the issued written > data will be lost. > > Therefore, in order to keep data consistency we need to flush the changes > to the L2 entry to the disk in time for the newly allocated cluster. > > Signed-off-by: Ying Fang <fangyi...@huawei.com>
If you want to have data safely written to the disk after each write request, you need to use cache=writethrough/directsync (in other words, aliases that are equivalent to setting -device ...,write-cache=off). Note that this will have a major impact on write performance. cache=none means bypassing the kernel page cache (O_DIRECT), but not flushing after each write request. Kevin
