[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Qemu-devel] [RFC] Disk integrity in QEMU
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] [RFC] Disk integrity in QEMU |
Date: |
Mon, 13 Oct 2008 08:42:51 +0200 |
User-agent: |
Mozilla-Thunderbird 2.0.0.16 (X11/20080724) |
Mark Wagner a écrit :
> Anthony Liguori wrote:
>> Mark Wagner wrote:
>>> If you stopped and listened to yourself, you'd see that you are making
>>> my point...
>>>
>>> AFAIK, QEMU is neither designed nor intended to be an Enterprise
>>> Storage Array,
>>> I thought this group is designing a virtualization layer. However,
>>> the persistent
>>> argument is that since Enterprise Storage products will often
>>> acknowledge a write
>>> before the data is actually on the disk, its OK for QEMU to do the same.
>> I think you're a little lost in this thread. We're going to have QEMU
>> only acknowledge writes when they complete. I've already sent out a
>> patch. Just waiting a couple days to let everyone give their input.
>>
> Actually, I'm just don't being clear enough in trying to point out that I
> don't think just setting a default value for "cache" goes far enough. My
> argument has nothing to do with the default value. It has to do with what the
> right thing to do is in specific situations regardless of the value of the
> cache setting.
>
> My point is that if a file is opened in the guest with the O_DIRECT (or
> O_DSYNC)
> then QEMU *must* honor that regardless of whatever value the current value of
> "cache" is.
>
> So, if the system admin for the host decides to set cache=on and something
> in the guest opens a file with O_DIRECT, I feel that it is a violation
> of the system call for the host to cache the write in its local cache w/o
> sending it immediately to the storage subsystem. It must get an ACK from
> the storage subsystem before it can return to the guest in order to preserve
> the guarantee.
>
> So, if your proposed default value for the cache is in effect, then O_DSYNC
> should provide the write-thru required by the guests use of O_DIRECT on the
> writes. However, if the default cache value is not used and its set to
> cache=on, and if the guest is using O_DIRECT or O_DSYNC, I feel there are
> issues that need to be addressed.
>
Everybody agrees that we should support data integrity *by default*. But
please admit that some persons have different needs than yours, and
actually *want* to lie to the guest. We should propose such and option,
with a *big warning*.
--
.''`. Aurelien Jarno | GPG: 1024D/F1BCDB73
: :' : Debian developer | Electrical Engineer
`. `' address@hidden | address@hidden
`- people.debian.org/~aurel32 | www.aurel32.net
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, (continued)
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Anthony Liguori, 2008/10/12
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, nuitari-qemu, 2008/10/12
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Mark Wagner, 2008/10/12
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Anthony Liguori, 2008/10/12
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Mark Wagner, 2008/10/12
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Anthony Liguori, 2008/10/12
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU,
Aurelien Jarno <=
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Steve Ofsthun, 2008/10/13
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Chris Wright, 2008/10/12
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Avi Kivity, 2008/10/12
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Dor Laor, 2008/10/12
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Jamie Lokier, 2008/10/12
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Anthony Liguori, 2008/10/12
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Anthony Liguori, 2008/10/12
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Andrea Arcangeli, 2008/10/15
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Anthony Liguori, 2008/10/12
- Re: [Qemu-devel] [RFC] Disk integrity in QEMU, Avi Kivity, 2008/10/12