[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.

[Alexandre DERUMIER]

>>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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