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Re: [Qemu-devel] scsi-hd with discard_granularity and unmap results in A


From: Stefan Priebe - Profihost AG
Subject: Re: [Qemu-devel] scsi-hd with discard_granularity and unmap results in Aborted Commands
Date: Mon, 19 Nov 2012 10:36:06 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121028 Thunderbird/16.0.2

Hi Paolo,

Am 19.11.2012 09:10, schrieb Paolo Bonzini:
I'm sorry the discard requests aren't failing. Qemu / Block driver
starts to cancel a bunch of requests.

That is being done in the kernel (the guest, I think) because the UNMAPs
are taking too long.

That makes sense. RBD handles discards as buffered I/O. When i do an mkfs.xfs on a 30GB device i see around 900 pending discard requests. rbd finishes them all before reporting success.

If it is correct that a 3.6.7 kernel sends as many discard requests i only the a solution in using unbuffered I/O for discards.

Do you know what is the correct way?

Greets,
Stefan



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