[dm-devel] [PATCH 0/3] freeze feature ver 1.8

[Takashi Sato]

Hi,

Alasdair G Kergon wrote:
>> Currently, ext3 in mainline Linux doesn't have the freeze feature which
>> suspends write requests.  So, we cannot take a backup which keeps
>> the filesystem's consistency with the storage device's features
>> (snapshot and replication) while it is mounted.
>> In many case, a commercial filesystem (e.g. VxFS) has
>> the freeze feature and it would be used to get the consistent backup.
>> If Linux's standard filesytem ext3 has the freeze feature, we can do it
>> without a commercial filesystem.
>
> Is the following a fair summary?

Yes, you are right.
We'd like to use the freeze feature without device-mapper/LVM.

> 1. Some filesystems have a freeze/thaw feature.  XFS exports this to
> userspace directly through a couple of ioctls, but other filesystems
> don't.  For filesystems on device-mapper block devices it is exported to
> userspace through the DM_DEV_SUSPEND ioctl which LVM uses.
>
> 2. There is a desire to access this feature from userspace on non-XFS
> filesystems without having to use device-mapper/LVM.
>
> Alasdair

Cheers, Takashi