On 08/31/2010 01:13 PM, Tejun Heo wrote: > Hello, > > On 08/31/2010 12:07 PM, Boaz Harrosh wrote: >> I don't know all the specifics of the virtio driver and the KVM backend but >> don't the KVM target io is eventually directed to a local file or device? >> If so the scsi device has disappeard but the bulk of the data is in host cache >> at the backstore (file or bdev). Once all files are closed the data is synced >> to disk. >> >> Is it not the same as Ric's problem of disconnecting the sata cable but >> not dropping power to the drive. The main of the cache is still intact. > > There are two layers of caching there. > > drive cache - host page cache - guest > > When guest issues FLUSH, qemu will translate it into fdatasync which > will flush the host page cache followed by FLUSH to the drive which > will flush the drive cache to the media. If you delete the host disk > device, it will be detached w/o host page cache flushed. So, although > it's not complete, it will lose good part of cache. With out write > out timeout increased and/or with laptop mode enabled, it will > probably lose most of cache. > Ha, ok you meant that device. So if you have a dedicated physical device for backstore that would be a very nice scriptable way. Thanks, that's a much better automated test than pulling drives out of sockets. > Thanks. > Boaz -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
