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Re: [Libguestfs] [PATCH] New tool: virt-format



On 01/17/2012 08:11 PM, Richard W.M. Jones wrote:
On Tue, Jan 17, 2012 at 07:58:15PM +0200, Török Edwin wrote:
- does it autodetect when disk is too large for MBR and GPT would be
    needed?

No, but you're right that it should do.  I'll make this change.

- does it align partitions to SSD erase block size? (LVM is
    particularly tricky to get right manually)

It aligns to 64K at the moment, for partitions.  For LVM we just use
the defaults, whatever they are.

I think you need to account for the LVM header size, there was a blog-post from Theodore Tso on this topic:
http://web.archive.org/web/20101130200444/http://thunk.org/tytso/blog/2009/02/20/aligning-filesystems-to-an-ssds-erase-block-size/

 I don't know if it is possible to
pass the SSD erase block size up through the virt stack.

I was thinking more about a command-line flag to specify alignment.
My SSD reports 512 bytes as both logical and physical sector size, and thats a physical drive.
Only my HDD reports a 4096 physical sector size (512 logical).


CC'd to Paolo Bonzini: Will virtio-scsi make this easier for us in
future?

  - can I specify a backing-file for qemu disks? (qcow, and qed I think)

Yes, in the sense that it just uses the qcow2 disk and doesn't attempt
to create one, so whatever backing-file etc settings are already on
the qcow2 disk are not modified in any way.

  - can --wipe use TRIM on SSDs instead of writing zeroes?

No.  This is a missing qemu feature which I've asked about a few
times, but until qemu and the rest of the virt stack implements it, we
won't have it in libguestfs (and conversely when it is implemented,
we'll most likely get it for free).

Paolo Bonzini: ^^ same question about virtio-scsi ^^

  - can I setup LVM striping and mirror with it?

No.  In general these are not exposed through libguestfs, although
they should be, and could be easily enough if someone wrote the patch.

Rich.



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