You can't do that, it doesn't work. The only way you can access the same block device from multiple hosts at the same time is if you use a cluster filesystem. Using a non-cluster filesystem like this is highly unsafe and will very likely quickly lead to total dataloss.
( I am a little bit surprised that you managed to mount ext4 from both hosts at the same time. ext4 SHOULD have put a SCSI [PERSISTENT] RESERVATION on the disk on the first mount in order to prevent a second host from accessing the device. Does btrfs put a reservation on the underlying SCSI device when it mounts the filesystem? If not, it should. ) If you want to share data read/write across multiple hosts you should either use a file server and a network file system such as NFS or CIFS. Or if you want to use block/iSCSI, then you must use a proper cluster filesystem of which there are several available for linux. regards ronnie sahlberg On Fri, Jun 27, 2014 at 8:44 AM, Zhe Zhang <zhe.zhang.resea...@gmail.com> wrote: > Hi, > > I setup 2 Linux servers to share the same device through iSCSI. Then I > created a btrfs on the device. Then I saw the problem that the 2 Linux > servers do not see a consistent file system image. > > Details: > -- Server 1 running kernel 2.6.32, server 2 running 3.2.1 > -- Both running btrfs v0.20-rc1 > -- Server 2 has device /dev/vdc, exposed as iSCSI target > -- Server 1 mounts the device as /dev/sda > -- Server 1 'mount /dev/sda /mnt/btrfs'; server 2 'mount /dev/vdc /mnt/btrfs', > -- When server 1 'touch /mnt/btrfs/foo', server 2 doesn't see any > file under /mnt/btrfs > -- I created /mnt/btrfs/foo on server 2 as well; then I added some > content from both server 1 and server 2 to /mnt/btrfs/foo > -- After that each server sees the content it adds, but not the > content from the other server > -- Both server 'umount /mnt/btrfs', and mount it again > -- Then both servers see /mnt/btrfs/foo with the content added from > server 2 (I guess it's because server 2 created the foo file later > than server 1). > > I did a similar test on ext4 and both servers see a consistent image > of the file system. When server 1 creates a foo file server 2 > immediately sees it. > > Is this how btrfs is supposed to work? > > Thanks, > > Zhe > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majord...@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
