linux-kernel - Re: [ANNOUNCE] Btrfs: a copy on write, snapshotting FS

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Date:	Thu, 14 Jun 2007 14:20:26 -0400
From:	Chuck Lever <chuck.lever@...cle.com>
To:	Chris Mason <chris.mason@...cle.com>
CC:	John Stoffel <john@...ffel.org>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [ANNOUNCE] Btrfs: a copy on write, snapshotting FS

Hi Chris-

John Stoffel wrote:
> As a user of Netapps, having quotas (if only for reporting purposes)
> and some way to migrate non-used files to slower/cheaper storage would
> be great.
> 
> Ie. being able to setup two pools, one being RAID6, the other being
> RAID1, where all currently accessed files are in the RAID1 setup, but
> if un-used get migrated to the RAID6 area.  
> 
> And of course some way for efficient backups and more importantly
> RESTORES of data which is segregated like this.  

I like the way dump and restore was handled in AFS (and now ZFS and 
NetApp).  There is a simple command to flatten a file system and send it 
to another system, which can receive it and re-expand it.  The 
dump/restore process uses snapshots and can easily send incremental 
backups which are significantly smaller than 0-level.  This is somewhat 
better than rsync, because you don't need checksums to discover what 
data has changed -- you already have the new data segregated into 
copied-on-write blocks.

NetApp happens to use the standard NDMP protocol for sending the 
flattened file system.  NetApp uses it for synchronous replication, 
volume migration, and back up to nearline storage and tape.  AFS used 
"vol dump" and "vol restore" for migration, replication, and back-up. 
ZFS has the "zfs send" and "zfs receive" commands that do basically the 
same (Eric Kustarz recently published a blog entry that described how 
these work).  And of course, all file system objects are able to be sent 
this way:  streams, xattrs, ACLs, and so on are all supported.

Note also that NFSv4 supports the idea of migrated or replicated file 
objects.  All that is needed to support it is a mechanism on the servers 
to actually move the data.

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