[pve-devel] [PATCH] Increases the dd read/write speed when migrating LVM disks. This should bring LVM migration speed up to match that of rsyncing qcows.

[Michael Rasmussen]

Default block equals logical block size so either 512B or 4k.

On August 23, 2016 12:16:49 PM GMT+02:00, Alexandre DERUMIER <aderumier at odiso.com> wrote:
>>>I think a value which can be handle by disk cache is ok. (1M should
>be large enough, if the disk can do 200iops, it's around 200MB/S) 
>
>Another thing to check , is the sparse option.
>
>If the block size is too high, the are more chance that they are datas
>inside the block, so it'll be full copied.
>
>What is the result with a 64k block size instead 1M ?  (I think the
>default bs is 512b, so 64k is already a huge improvement)
>
>----- Mail original -----
>De: "aderumier" <aderumier at odiso.com>
>À: "dietmar" <dietmar at proxmox.com>, "pve-devel"
><pve-devel at pve.proxmox.com>
>Cc: "jlavoy" <jalavoy at gmail.com>
>Envoyé: Mardi 23 Août 2016 12:12:17
>Objet: Re: [pve-devel] [PATCH] Increases the dd read/write speed when
>migrating LVM disks. This should bring LVM migration speed up to match
>that of rsyncing qcows.
>
>>>IMHO a block size of 64MB is a bit too large. I guess you can see the
>same 
>>>speed improvements with much smaller sizes - mabe 1M is large enough?
>
>
>I think a value which can be handle by disk cache is ok. (1M should be
>large enough, if the disk can do 200iops, it's around 200MB/S) 
>
>----- Mail original ----- 
>De: "dietmar" <dietmar at proxmox.com> 
>À: "jlavoy" <jalavoy at gmail.com>, "pve-devel"
><pve-devel at pve.proxmox.com> 
>Envoyé: Mardi 23 Août 2016 10:26:38 
>Objet: Re: [pve-devel] [PATCH] Increases the dd read/write speed when
>migrating LVM disks. This should bring LVM migration speed up to match
>that of rsyncing qcows. 
>
>> + run_command([["dd", "if=$src", "bs=64M"],["/usr/bin/ssh", 
>> "root\@${target_host}", 
>> + "dd", 'conv=sparse', "of=$dst", "bs=64M"]]); 
>
>IMHO a block size of 64MB is a bit too large. I guess you can see the
>same 
>speed improvements with much smaller sizes - mabe 1M is large enough? 
>
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