Status: New
Owner: ----
New issue 412 by [email protected]: dd oflag=dsync and 64k limits the
copy speed too much
http://code.google.com/p/ganeti/issues/detail?id=412
What software version are you running? Please provide the output of "gnt-
cluster --version" and "gnt-cluster version".
gnt-cluster (ganeti v2.6.2) 2.6.2
Software version: 2.6.2
Internode protocol: 2060000
Configuration format: 2060000
OS api version: 20
Export interface: 0
What distribution are you using?
Gentoo
Linux 3.5.3 Vanilla
OpenSSH_5.9p1-hpn13v11, OpenSSL 1.0.0j 10 May 2012
What steps will reproduce the problem?
1. gnt-instance move instance1
What is the expected output? What do you see instead?
When using '$ gnt-instance move instance1' the copy speed on a 1Gbit/s
network is around 1-2MB/s. At least in my setup.
With '$ ssh [email protected] 'dd if=/dev/drbd0 bs=100M' | dd
of=/dev/drbd0' the speed is around ~40MB/s.
This is due to, (backend.py)
# we set here a smaller block size as, due to ssh buffering, more
# than 64-128k will mostly ignored; we use nocreat to fail if the
# device is not already there or we pass a wrong path; we use
# notrunc to no attempt truncate on an LV device; we use oflag=dsync
# to not buffer too much memory; this means that at best, we flush
# every 64k, which will not be very fast
destcmd = utils.BuildShellCmd("dd of=%s conv=nocreat,notrunc bs=65536"
" oflag=dsync", dest_path)
Please provide any additional information below.
This makes '$ gnt-instance move' too slow that it can't be used.
# ... we use oflag=dsync
# to not buffer too much memory; this means that at best, we flush
# every 64k, which will not be very fast
I don't think that is a valid factor. It makes the command unusable.
Those options should be reevaluated.
The hpn patches for ssh might affect the performance.
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