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From: | Paul Brook |
Subject: | Re: [Qemu-devel] [PATCH] virtio-spec: document block CMD and FLUSH |
Date: | Tue, 20 Apr 2010 14:22:58 +0100 |
User-agent: | KMail/1.12.4 (Linux/2.6.33-2-amd64; KDE/4.3.4; x86_64; ; ) |
> Does this mean that virtio-blk supports all three combinations? > > 1. FLUSH that isn't a barrier > 2. FLUSH that is also a barrier > 3. Barrier that is not a flush > > 1 is good for fsync-like operations; > 2 is good for journalling-like ordered operations. > 3 sounds like it doesn't mean a lot as the host cache provides no > guarantees and has no ordering facility that can be used. (3) allows the guest to queue overlapping transfers with well defined results. I have no idea how useful this is in practice, but it's certainly plausible. Paul
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