On Sun, Apr 12, 2009 at 10:32 PM, Sébastien Wacquiez <sw@xxxxxxxx> wrote: > Andrey Kuzmin a écrit : >> >> zvol (interface) does not just 'export raw device' but rather >> implements volume abstraction and integrates volume management into >> file-system. >> > > Yep. I suck at writing english, thanks for pointing that out :) > > I surely mislead myself, but I think that the "volume management" of ZFS > could be done with file. Basically volume abstraction aims to provide a layer above raw device implementing extra functionality not found with raw disk (e.g., fault-tolerance), expandability (one can add disks to a volume as needed) and single point of control over a bunch of disks. > > Alloc on write ? Use sparse file. Resizing ? Append or truncate the file. > Snapshot ? Snapshot the file. Another Volume ? An other file :) Basically you're right and, for instance, (deprecated) opensolaris user-spce iSCSI target supports exporting a regular zfs file to remote clients as raw scsi block device. At the same time, implementing a 'volume' on-top of a regular zfs file might be unsafe (file-system makes some assumptions wrt I/O that are fine with raw devices below real volume but do not necessarily hold for a regular file) . > > In fact, the two thinks that have to be done, for me, is : > 1/ Optimise the different layer to bypass permission, acl, & co, and surely > the way data is written. > 2/ Be able to export those file directly as block device. (Allowing some > more optimisation :) ) > > It's why I called this feature "export raw device" (as in "export raw file > as block device"). As I say, it could be emulated with file and loopback, > but it'll surely be slow ... So I wanna know if btrfs plan to have those > type of optimization (and the user land tools to simplify it's management). > That's a question to linux-btrfs@, I'm quite new to this one. Regards, Andrey > > Regards, > > > Sébastien Wacquiez > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > 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 majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
