Mailinglist Archive: opensuse (1382 mails)

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Re: [opensuse] [OT] is there a virtual machine that uses harddisk as harddisk image
  • From: Anders Johansson <ajohansson@xxxxxxx>
  • Date: Mon, 1 Jun 2009 18:12:12 +0200
  • Message-id: <200906011812.13070.ajohansson@xxxxxxx>
On Monday 01 June 2009 18:03:38 Randall R Schulz wrote:
On Monday June 1 2009, Anders Johansson wrote:
On Monday 01 June 2009 17:23:42 Randall R Schulz wrote:
Do you know any block devices these days that aren't disks or flash
drives?

Optical devices (CD, DVD, BluRay), iSCSI, FCoE, ATAoE, nbd, loopback
devices, ram disks

And how many of them (that are not in fact disks or intermediaries to
disks) are suitable for acting as the physical storage for a VMware
virtual disk? Certainly not any of the optical types.

Aside from performance, why not? Most of the time a disk doesn't even have to
be writable. It is perfectly possible to have almost all your file system
running on a DVD (for example), though from a performance perspective perhaps
not desirable

The rest are
interconnects or mediators to some physical storage. If that storage
isn't random access (disk), then it's not suitable as the physical
representation of a virtual machine's virtual disk.

The way you write "random access (disk)" makes me think you somehow equate the
two, and obviously if you say "anything that is usable as a root device is by
definition a disk" then it is obviously a disk. But I don't accept that
equality. The point was that any block device can be used, simply because they
behave in a sufficiently equivalent way.

None of the ones I listed are disks, but they share behaviour with disks, not
because they are disks in any way, but because they speak the same
communication protocols as disks of various types. What is at the other end of
that protocol is supposed to be a black box, as long as it fulfills the
semantics of the protocol.

I'm pretty sure DECtape is officially obsolete.

I have seen people export tape devices as nfs shares. Not sure what
brand it was, but it seemed to work (but slooooow of course :)

Magnetic tape (of the standard 9-track variety, at least) is not
rewritable because the drive does not ensure that a new record
precisely aligns with the one being overwritten.

As I said, I don't know what they were using exactly, but it was definitely a
tape drive of some kind. Not to be recommended, of course

Anders
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