LXC migration - ssh compression on/off

zima

Active Member
Nov 7, 2014
42
7
28
Hi,
Usualy migration do not exceed 12MB/s because of the option -C in ssh.
I understand that compression is good in case of copying free space. But in normal use, when containers don't have huge amount of free space, speeds without compression are far more greater and benefits from compression dissapear completely if container have a lot of data.

After removing -C in Storage.pm migration achieved 109MB/s - utilize full Gbit link.
Taking this into account, transfering 100GB volume with 20GB data is few times faster than with default compression on.

Quick test on container with 4GB volume with 0.5GB data:
with -C: 4294967296 bytes (4.3 GB) copied, 66.9362 s, 64.2 MB/s (duration 00:01:12)
without -C: 4294967296 bytes (4.3 GB) copied, 39.5482 s, 109 MB/s (duration 00:00:43)

Maybe we can add option to enable/disable compression in migration dialog?
 

wbumiller

Proxmox Staff Member
Staff member
Jun 23, 2015
647
87
48
Right, -C is for slow connections and apparently not very fast. I wonder though if it makes sense to put a gzip/lzop/... in between dd and ssh, that way the compression is at least a separate process (AFAIK ssh is otherwise single threaded). But as an option of course.

Also we should probably send a SIGUSR1 every couple of seconds to dd to get some progress output in this case, since currently you see that the volume is created and then a whole lot of nothing before some time later it finishes.
 

zima

Active Member
Nov 7, 2014
42
7
28
I also changed cipher in ssh between cluster members to arcfour and getting 1gbit/s instead of 0.5Gbit/s even with old x7560 (max is 1.2Gbit/s) . New cpus achieves +5gbit/s speeds with single ssh thread.
 

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