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Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD |
Date: |
Mon, 18 Mar 2013 09:31:59 +0100 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130219 Thunderbird/17.0.3 |
Il 17/03/2013 19:54, Peter Maydell ha scritto:
> On 17 March 2013 18:51, Paolo Bonzini <address@hidden> wrote:
>> Il 17/03/2013 01:04, Aurelien Jarno ha scritto:
>>> | boot | install build-dep | build lm-sensors |
>>> ------------------------+------+-------------------+------------------+
>>> versatile | 1:09 | 2:27 | 4:09 |
>>> versatile cache=wb | 1:08 | 2:25 | 3:44 |
>>
>> Strange, cache=wb should be the default.
>>
>> The real problem with SD is that it doesn't have a flush command, hence
>> it cannot be made safe against power losses.
>
> So, two things here:
> (a) the way to make it safe against power loss is that when the
> guest writes a block of data it has to really hit the emulated
> disk, because this is how the hardware works
> (b) I thought this was the reason cache=wb wasn't the default (ie
> that we weren't defaulting to 'may lose data on powerloss').
See the commit message that Aurelien posted. The combination of
"virtio-blk will auto-toggle to writethrough on very old kernels",
"guests can toggle it for all of IDE/SCSI/virtio", "memory cards are
anyway unusable with writethrough" finally made the balance tilt in
favor of cache=wb.
Paolo
- Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD, (continued)
- Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD, Peter Maydell, 2013/03/15
- Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD, Aurelien Jarno, 2013/03/15
- Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD, Peter Maydell, 2013/03/15
- Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD, Aurelien Jarno, 2013/03/16
- Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD, Peter Maydell, 2013/03/16
- Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD, Aurelien Jarno, 2013/03/17
- Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD, Peter Maydell, 2013/03/17
- Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD, Paolo Bonzini, 2013/03/17
- Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD, Peter Maydell, 2013/03/17
- Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD, Aurelien Jarno, 2013/03/17
- Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD,
Paolo Bonzini <=
- Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD, Aurelien Jarno, 2013/03/17
- Re: [Qemu-devel] [PATCH] hw/vexpress: set default block type to SD, Paolo Bonzini, 2013/03/17