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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] [RFC] block-queue: Delay and batch metadata writes |
Date: | Mon, 20 Sep 2010 10:51:47 -0500 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.12) Gecko/20100826 Lightning/1.0b1 Thunderbird/3.0.7 |
On 09/20/2010 10:08 AM, Kevin Wolf wrote:
If you're comfortable with a writeback cache for metadata, then you should also be comfortable with a writeback cache for data in which case, cache=writeback is the answer.Well, there is a difference: We don't pollute the host page cache with guest data and we don't get a virtual "disk cache" as big as the host RAM, but only a very limited queue of metadata.
Would it be a mortal sin to open the file twice and have a cache=none version for data and cache=writeback for metadata?
The two definitely aren't consistent with each other but I think the whole point here is that we don't care.
It opens up some other possibilities too like cache=none for data and cache=writethrough for metadata which may be a useful combination.
Regards, Anthony Liguori
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