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Re: [Qemu-block] [PATCH 4/4] block: Cater to iscsi with non-power-of-2 d

From: Eric Blake
Subject: Re: [Qemu-block] [PATCH 4/4] block: Cater to iscsi with non-power-of-2 discard
Date: Tue, 25 Oct 2016 08:59:57 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0

On 10/25/2016 07:42 AM, Peter Lieven wrote:
>> But hey, that firmware is seriously weird. :)
> Yes, so you would not change the new implementation?
> Even if the discard is e.g. 1MB it could theretically be that internally
> the device has a finer granularity. Its an optimal discard alignment
> not the minimum required discard size. I think thats a difference.
> It does not say I can't handle smaller discards.

The firmware is probably technically buggy for advertising too large of
a minimum granularity, if it can piece together smaller requests into a
larger discard.  If discards need to happen at a smaller granularity,
the firmware (or kernel quirk system) should fix the advertisement to
the actual granularity that it will honor.  I don't see a reason to
change qemu's current behavior.

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

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