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[linux-lvm] Poor LVM dump performance



Hi everyone,

I've run into som substantial read degredation when using dump or tar
to backup filesystems that are stored on LVM2 LVs.  Many times in the
past I have seen dump run at speeds approaching block device speeds;
50-60MiB/s, similar with tar.

I'm seeing speeds in the range of 3-4MiB/s when dumping a filesystem.
If I increase dump's blocksize to 128KiB records, speed jumps up to
about 20KiB/s, which is better but still frustratingly slow.  Going
to 1024KiB gets me about 28MiB/s.

Is this amount of performance loss expected?  My LV is just two SATA
hard disks that I put into a VG.  Stupid benchmarks with dd gives me a
raw read speed from the LV of about 60MiB/sec.

Any ideas on what's slowing down dump?


-- 
Ross Vandegrift
ross kallisti us

"The good Christian should beware of mathematicians, and all those who
make empty prophecies. The danger already exists that the mathematicians
have made a covenant with the devil to darken the spirit and to confine
man in the bonds of Hell."
	--St. Augustine, De Genesi ad Litteram, Book II, xviii, 37


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