About Filesystem freeze/thaw in freebsd

[Charles Sprickman]

On Feb 16, 2015, at 4:54 AM, Konstantin Belousov <kostikbel at gmail.com> wrote:

> On Mon, Feb 16, 2015 at 09:31:58AM +0000, Matthew Seaman wrote:
>> On 02/16/15 09:07, zx zx wrote:
>>> Hi,               I am experimenting to do a live backup of FreeBSD
>>> VM. Question is do we have freeze/thaw interfaces in FreeBSD? I
>>> searched a lot in web and freebsd source code, just could not find
>>> the right interface.               As I know that in linux:VxFS
>>> provides ioctl interfaces to application programs to freeze and thaw
>>> VxFS file systems. The interfaces are VX_FREEZE, VX_FREEZE_ALL, and
>>> VX_THAW.About Freeze and thaw Freezing a file system temporarily
>>> blocks all I/O operations to a file system and then performs a sync
>>> on the file system. Current operations are completed and the file
>>> system is synchronized to disk. Freezing a file system is a necessary
>>> step for obtaining a stable and consistent image of the file system
>>> at the volume level. Consistent volume-level file system images can
>>> be obtained and used with a file system snapshot tool. The freeze
>>> operation flushes all buffers and pages in the file system cache that
>>> contain dirty metadata and user data. The operation then suspends any
>>> new activity on the file system until the file system is thawed.
>>> Any help would be appreciated, thanks a lot!  Andy Zhang
>> 
>> What you want is snapshotting.  You can create a snapshot of UFS or ZFS
>> filesystems, mount the snapshot and then back it up without needing to
>> worry about the filesystem changing while you're trying to back it up.
>> 
>> See mksnap_ffs(8) and the 'snapshot' entry in zfs(8)
>> 
>> The snapshot is mounted separately from the actual filesystem which can
>> carry on with normal activities in the mean time.
>> 
>> Snapshotting functionality is built into dump(8) for UFS filesystems
>> (See the -L flag in that man page) or you can use zfs send / recv to
>> dump filesystems to tape, which implies use of snapshots.
> 
> Snapshot is different functionality from what the OP asked.
> Exactly requested feature is provided by UFSSUSPEND/UFSRESUME ioctls
> on the /dev/ufssuspend, for UFS volumes.  You should consult the code
> to see how to use them.

Do the VMWare tools currently implement this?

VMWare doesnt complain when making snapshots, but I never found a
way to verify its actually working.

How about Xen and popular Xen variations like Amazon and Digital Ocean?

Thanks,


Charles

> 
> I suspect that the similar feature exists for ZFS, but I do not know
> where to start looking.
> _______________________________________________
> freebsd-fs at freebsd.org mailing list
> http://lists.freebsd.org/mailman/listinfo/freebsd-fs
> To unsubscribe, send any mail to "freebsd-fs-unsubscribe at freebsd.org"