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Re: [Qemu-devel] [PATCH] Further tidy-up on block status
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [PATCH] Further tidy-up on block status |
Date: |
Fri, 20 Jan 2017 13:35:10 -0600 |
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Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0 |
On 01/20/2017 12:00 PM, Alex Bligh wrote:
>
>> On 20 Jan 2017, at 17:04, Vladimir Sementsov-Ogievskiy <address@hidden>
>> wrote:
>>
>> About extents: is 32bit length enough? We will have to send 4096 for empty
>> 16tb disk..
>
> The nbd protocol uniformly uses 32 bit lengths (for better or for worse).
> This is baked into the specification heavily.
>
> I'm not sure sending 4,096 items for an empty 16TB disk is any great hardship
> to be honest.
If it truly matters, an idea that has already been floated on the list
is to add a new NBD_CMD_FLAG_SCALE (or some other spelling) that states
that a particular command is sending lengths scaled by a particular
factor (by the block size? obviously it would have to be better
specified). Under this idea, the scaling factor would allow you to
report larger extents for fewer back-and-forth operations, but it gets
tricky if the scaling is allowed to get larger than the minimum
granularity between extent changes.
The other idea that has been floated is a way to report whether the
entire export is known to be all-zero content at the time the client
connects, which would trade 4096+ queries (you'd actually have to do
more than 4096 queries, since length is < 4G, not <= 4G) with a single
piece of information at the time the client connects.
Either way, discussion on such enhancements are probably worth a new thread.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- Re: [Qemu-devel] [PATCH] Further tidy-up on block status, (continued)
Re: [Qemu-devel] [PATCH] Further tidy-up on block status, Vladimir Sementsov-Ogievskiy, 2017/01/12
Re: [Qemu-devel] [PATCH] Further tidy-up on block status, Vladimir Sementsov-Ogievskiy, 2017/01/20