libvirt users - Mar 2013 - SSD Trim needed? Physical Block Device Keep Track Of Guest FS Blocks?

I am trying to figure out if a SSD drive needs to receive trim commands from the
KVM guest filesystem(strictly Linux ext4 in this case)....

When a file is deleted inside a KVM guest(ext4 and raw image)....If a SSD is the
underlying block device that the KVM raw disk image resides on, does the SDD
drive need to know which block(s) are marked for reuse within the raw image? ?Or
is it since the Guest raw image is a container that the physical hard drive has
no concern about the filesystem blocks within the Guest? Meaning the physical
disk would only be concerned with the image itself as a whole...such as if the
whole image was deleted?

Thanks,
-Darin
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On 03/17/2013 05:15 AM, d hee wrote:
> I am trying to figure out if a SSD drive needs to receive trim commands
from the KVM guest filesystem(strictly Linux ext4 in this case)....
> 
> When a file is deleted inside a KVM guest(ext4 and raw image)....If a SSD
is the underlying block device that the KVM raw disk image resides on, does the
SDD drive need to know which block(s) are marked for reuse within the raw image?
Or is it since the Guest raw image is a container that the physical hard drive
has no concern about the filesystem blocks within the Guest? Meaning the
physical disk would only be concerned with the image itself as a whole...such as
if the whole image was deleted?
[Any way you can convince your mailer to wrap long lines?]

Upstream qemu is hoping to add new options to control how far a TRIM
command in a guest is propagated back to the host storage, whether raw
file or block device in the host.  Paolo Bonzini is spear-heading that
effort.  But until qemu 1.5 is released with more options for
controlling what happens, we don't yet have the libvirt design in place
to expose those options.

https://lists.gnu.org/archive/html/qemu-devel/2013-02/msg01252.html

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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