-----Original Message----- From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com]On Behalf Of Steve Losen Sent: Thursday, December 12, 2002 1:37 PM To: Chuck Tomasi Cc: 'Mitko Blazeski'; 'Kumar, Rahul'; 'toasters@mathworks.com' Subject: Re: file folding impact
My question about file folding (after reading about it here and
on NOW)...
Why would a block end up in a snapshot if it is the same as the previous snapshot? Isn't the point of snapshots only to save the 'old
version' of
blocks that have been changed?
Snapshots do not copy any blocks, so including the same block in multiple snapshots incurs no overhead. It works like this. Each data block in a volume has associated with it a bit map of length 32 (20 on older releases) These bits correspond to snapshots. For example, if bit #3 is set, then the block is part of snapshot #3. The filer keeps track of which logical name (eg "hourly.0") is associated with each bit. The size of the bit map limits the number of snapshots that can exist in a volume.
[snip...]
Ok, all of that makes sense to me. But I am still unclear on what filefolding does exactly.
This explanation fits in well with how I think, so if someone could present the basic concept of filefolding in a similar matter, I would very much appreciate it. :)
Thanks, Jordan