Coda File System


From: Quinn Weaver <>
Date: Thu, 13 Jan 2000 18:53:15 -0800 (PST)

In setting up Coda, I noticed that the backup scripts depend on dump.
This is a problem for the use of Coda I have planned, since it requires
a quiescent filesystem.  I was wondering whether anyone has experimented
with backup methods that can be used while the filesystem is active, like
tar.  This leads to two questions:

1) Is this possible?  My understanding is that metadata are kept in the
cache, not in regular files on the Coda filesystem, so I am afraid that
tar (and any other file-oriented backup tool) will be unable to back up

2) Even if tar can back up metadata, there is the question of keeping the
metadata consistent with the state of the filesystem.  I can imagine a
case where the metadata have a record of an impending write, and you back
up that record, and then the write occurs.  In that case, your backup
would contain a copy of the file from after the write, but it would have
a record that the write still needed to be made.  There would be an
inconsistency.  I suppose that, if you restored such a backup, Coda would
complain and you would have to fix a bunch of stuff.

This is a fundamental problem with interactive back-ups of journaling
filesystems, so I'm sure someone has solved it.  Can someone  please
explain the solution?

On the other hand, if my premise in question 2--that tar can see
metadata--is wrong, please tell me! ;)

If other people have pondered these problems, I would greatly appreciate
hearing from them.

Quinn Weaver  Software Engineer  ,      Vovida Networks
"I'm swingin' swords          o-=*|>>>>>>>>>>            ===()==========>     
  Strictly based on keyboards".  '         --The RZA             <==()==  
Received on 2000-01-13 21:49:07