6MB/s disk -to- disk write speed using cp ... (but 90+MB/s ftp over Gb lan)

[capndave]

I went to copy from local disk to local disk (using cp -R) and was getting
6MB/s speeds. It upped to 15MB/s with a large, single 500MB files. I get
90+MB/s write speed to these *same drives* via ftp over the Gb lan.

[root@freenas]cp -R /mnt/disk1 /mnt/disk2

I'm no expert, but I'm not sure why my internal disk->disk transfers
are so cripplingly slow using cp.

Note - I tested transfers to the other 2 local disks on this box and it was the same.

Disks are connected to motherboard SATA ports, not via a peripheral card.

Core DUO E6600 4GB RAM
FreeNAS 8.0.3 64-bit
Disk1 3Gbps, 1.5TB, 7200rpm, ZFS
Disk2 3Gbps, 2TB, 7200rpm, ZFS - Clean disk.

 

[pk007_za]

I've seen this before on a non-FreeNAS system.

the SATA ports were all connected on a single pci-e 1x lane, meaning that reads would work great (reading is inherently faster than writing) but as soon as 2 x disks were used, over the single data channel, things would clog down. Think of it as your SATA bandwidth halving when 2 drives are used, and writing being 50% more resource intensive than reading

Higher quality boards alleviate this by dedicating more PCI-E lanes to sata ports.

Hope that helps.

Pk