On Dec 11, 2007, at 2:58 PM, Josh Wisenbaker wrote:
My guess is that while they are open encrypted disk images are not
in a consistent state. Things probably go through a couple of
caches, and there are constant writes to the disk image. Since it
is all one file TimeMachine would have to try and backup the very
large image each time (so that would eat disproportionally into
your space), and would probably have trouble completing the read
before something else tried to write into the space (causing a bit
of a nightmare).
In 10.5 FV images are sparsebundles, not plain sparse. This means
that each band of the image is a separate file and it should help
speed up the TM backups.
Thanks for that bit of information! That is probably going to prove
useful somewhere.
That probably helps out quite a bit from the TimeMachine perspective
(both on lessening the chances that you will be writing to that stripe
of the disk, and from the perspective on how often the files change),
but I still think that the unpredictable nature of when a relatively
large open file (that is the sum of the information that you want
backed up) that might get written to at any time probably is what
scared the engineers at Apple off doing this on the first go-around.
