Lession Learnt: DS1010+/1812+: rsync extremely slow

[phlo]

While writing out this post, I decided to take a look around and run a couple of benchmarks; in the process I found a solution for my problem. I'll still post, just in case someone should run into the same issues I did.
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Hi there

I've been a satisfied owner of a DS1010+ w/expansion for a couple of years now, but growing capacity needs and failing disks are forcing me to step up to a DS1812+. Both DSes run the current DSM 4.0 (2216); the DS1010+ is running a degraded RAID 6 on ten 2 TB WDs (one of which recently died); the DS1812+ has a newly installed SHR-2 on 7x3 TB and 1x2 TB. The odd 2 TB drive is in there make sure I'll be able to expand the SHR-2 volume to 8x3 TB plus a full 5x2 TB expansion bay. All drives' partitions are correctly aligned to 4K boundaries.

On to my problem: Transfer speeds from the DS1010+ to the DS1812+ are dysmally slow. Right now, I'm working with rsync through ssh and can't seem to exceed some 4 MB/s. I've upped the MTU to 9000, linked the DSes directly through a crosslink cable -- the transfer speed doesn't seem to pick up.

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Solution: After a bit of experimentation, I decided to try to use rsync in the rsync protocol mode (i.e. rsync --daemon on the DS1010+, rsync root@...::Share_Name on the DS1812+). I got around 3.5 MB/s, but also noticed rsync --daemon occupying around 24.5% CPU, which basically means it used 100% of one Core on the DS1010+'s Atom D510.
Up to that point, I had always used rsync with my standard set of params: -avz, with the "z" enabling compression. Skipping that, and just running rsync -av (archive, verbose), transfer speed is up to some 40-45 MB/s at around 19% of daemon CPU use. I've some other things on my mind right now, but --whole-file might hold some further optimization potential.

Anyhow, lession learnt: Skip compression if you're on an Atom CPU and GigE

[Ettepet]

I would advise against spanning a volume over the main unit and expansion unit. Any time the connection between the units fails or if the expansion unit is (remains) switched off while the spanning volume is (still) active your volume will become unusable. You might each time be forced to enter a Synology support form so this can (hopefully) be fixed.

You can speed up transfer if you use 2 ip connections between the DS1010 and the DS1812+, 1 like you have now (connected to switch/router) and the other one with static ip's in a different ip range from the main connection. No need for binding the connections with Link Aggregation or other, just make sure you enter valid static connection settings in a different range from the current one. I use drag-and-drop copying in File Station to 2 remote folders created on the copying side.