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Re: [PATCH] Allow NBD to be used locally

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From: Jan Engelhardt <jengelh@...>
To: Pavel Machek <pavel@...>
Cc: Laurent Vivier <Laurent.Vivier@...>, <Paul.Clements@...>, <nbd-general@...>, <linux-kernel@...>
Subject: Re: [PATCH] Allow NBD to be used locally
Date: Saturday, February 2, 2008 - 7:52 am

On Feb 2 2008 12:23, Pavel Machek wrote:

Local NBD is good for when the content you want to make available
through the block device is dynamic (generated on-the-fly),
non-linear or supersparse.

Take for example VMware virtual disks. Just a guess, but
they roughly can look like this:

  kilobytes  0.. 1: header
  kilobytes  1..10: correspond to LBA 0..20
  kilobytes 11..20: correspond to LBA 40..60
  kilobytes 21..22: correspond to LBA 22..23

So what we have is non-linearity -- LBA 22 comes after LBA 40 -- loop
does not deal with that.

And there is supersparsity -- the VMDK file itself is complete, but
unallocated regions like LBA 24..40 are sparse/zero when projected
onto a file/block device, respectively; loop cannot deal with that
either.

In fact, VMware uses local nbd today for its vmware-loop helper
utility, most likely because of the above-mentioned reasons. (Though
it quite often hung last time I tried.)
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Messages in current thread:
[PATCH] Allow NBD to be used locally, Laurent Vivier, (Fri Feb 1, 9:25 am)
Re: [PATCH] Allow NBD to be used locally, Pavel Machek, (Sat Feb 2, 7:23 am)
Re: [PATCH] Allow NBD to be used locally, Laurent Vivier, (Sat Feb 2, 11:26 am)
Re: [PATCH] Allow NBD to be used locally, Pavel Machek, (Sat Feb 2, 4:54 pm)
Re: [PATCH] Allow NBD to be used locally, Miklos Szeredi, (Sat Feb 2, 12:13 pm)
Re: [PATCH] Allow NBD to be used locally, Jan Engelhardt, (Sat Feb 2, 7:52 am)