On 17 Jun 2015, at 14:03, Perttu wrote:
On 17 Jun 2015 at 14:43:27, Paul Sture ([email protected]) wrote:
In an office environment where the majority of files are docx,
xlsx,
pptx or their equivalents in non-MS Office products, they are
already
compressed, so there's little point in applying compression at the
file
level. This is easily demonstrated via "unzip -l" on one of those
files.
File fragmentation is also an issue (I'm thinking of Windows here).
If
the guest system is unaware that its files are on a host system,
there
may well be a substantial CPU overhead dealing with what it thinks
are
fragmented files because; it's not just a matter of disk head
movement,
the guest OS has to handle the mapping to all those file
fragments.
Do you mean that Windows might do automatic reordering on the fly if
it
thinks files are too fragmented?
No, I'm thinking of the fragmentation itself, which occurs naturally in
Windows as files are created and deleted. Windows has to manage the
fact
that files are fragmented and that can be CPU intensive. This is a
little
known overhead on top of the physical disk head movement associated with
file
fragmentation on traditional disks.
I'd better explain where I'm coming from here. Back in the day I was
using
VMS, and that has monitoring tools which show the amount of CPU involved
in mapping to fragmented files. That mapping happens in kernel mode,
which has
the highest priority, so an unprivileged user working with badly
fragmented
files could severely affect performance for everyone else.
Yes CPUs are a lot faster nowadays so it should be less of an issue, but
it's still something to be aware of.
FWIW I have Windows 8.1 running under VMware Fusion and that will try to
expand the sparse disk image its running in to its full extent each time
I fire it up (VMware Fusion has a facility for reclaiming that space,
which I do run to save disk space). I haven't seen this issue with
and of the Windows Server variants I've run.
--
Paul Sture
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