A properly implemented snapshot system (such as network appliance almost
is) not only saves the inode info at the time of the snapshot, but also
saves the contents of blocks that are changed after the snapshot.
The end result is that storage costs are relitivly small for files that
are appended (a copy of the inode entries and a copy of the last block of
the file). for database files taht are truly random access storage costs
can go through the roof.
David Lang
P.S. the reason I say network appliance almost has it done right is that
there are problems in retreiving a file from a snapshot if you have
another copy of the same file (under a different name but using the same
inodes) on your current version. This has to do with improperly assigned
NFS tokens. I spent several hours last night fighting this issue.
On Thu, 1 Oct 1998, Stephen C. Tweedie wrote:
>
> It's a mistake to think that snapshots are equivalent to archived files!
> While it is certainly a valid viewpoint if you only consider creating
> and deleting files, the two concepts become radically different if you
> consider modifying existing files.
>
-----BEGIN PGP SIGNATURE-----
Version: PGP for Personal Privacy 5.0
Charset: noconv
iQEVAwUBNhO89T7msCGEppcbAQGaeAf9Hie6JuvImriMVexjzc0fiuWB/D/RlYKi
Zq2I2xJyqpOtbWN2Bx9sIYHpGAVdkf07LB/p72D+ldOWRiRNOBVL3tCxUWWj//OA
RrPfY4cSBEzH6MUSoFrGcnx6eHjf1qPlO4NwnDTjlROFTPT9SW7Cqw63lkAX3wzt
8TLFY1uaQfsuHSghIqfItwybWOLnWeHJFklWuU+wBnbo5cf48S0CZW9x0bx89tA5
2VVd1klWBa8ut6srH+nM5iKEpGbhNY1+yXxuHg1URWv3eZw6OOQIyffjDHjdapDP
fBuJ/Iv8LFFZW61LrEv3flvJXw3OZZozo0ul3ctfouc4GloCA5KB8w==
=nH1U
-----END PGP SIGNATURE-----
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.rutgers.edu
Please read the FAQ at http://www.tux.org/lkml/