rsync speedup - how ?

devzero at devzero at
Thu Aug 6 12:15:39 MDT 2009


i`m using rsync to sync large virtual machine files from one esx server to another. 

rsync is running inside the so called "esx console" which is basically a specially crafted linux vm with some restrictions.

the speed is "reasonable", but i guess it`s not the optimum - at least i donŽt know where the bottleneck is.

i`m not using ssh as transport but run rsync in deamon mode on the target. so this speeds things up if large amounts of data go over the wire.

i read that rsync would be not very efficient with ultra-large files (i`m syncing files with up to 80gb size)

regarding the bottleneck:  neither cpu, network or disk is at their limits - neither on the source nor on the destination system.
i don`t see 100% cpu, i don`t see 100% network or 100% disk i/o usage

furthermore, i wonder:
isn`t rsync just too intelligent for such file transfers, as the position of data inside that files (containing harddisk-images) won`t really change?
i.e. we don`t need to check for data relocation, we just need to know if some blocks changed inside a block of size "x" and if there was a change, we could transfer that whole block again. so i wonder if we need a "rolling checksum" at all to handle this. wouldn`t checksums over fixed block size be sufficient for this task? 


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