Drobo

Odd speed/CPU drop outs with a DroboPro/G-SPEED esPro setup

I haven’t opened a support ticket about this because I’m not sure if it’s a DRI, G-Technology or Apple issue. I’m leaning toward Apple.

Here’s my setup at work:

MacPro:
2 x DroboPro connected via FW800 and daisy chained to one another
2 x G-Technology G-SPEED esPro (RAID-10) connected via mini-SAS to a PCIe card, which System Profiler sees as two SCSI LUNs

The other computers there that connect to this ad-hoc server setup are also MacPro’s, with everything running 10.6.5.

The G-SPEED can handle about 600MB/sec read/write in this config and I use the DroboPro’s for archival storage. However, if I initiate simultaneous transfer on both a DroboPro and the G-SPEED on the same system over the network, the speeds plummet by 10x or more. The weirder thing is, say I’m rendering a movie out in Final Cut Pro (using the G-SPEED as the project files location and export location) and it’s using about 80% of the CPU on an octo-core machine, if I then start to copy to/from a DroboPro on that same machine, the CPU activity will start to just drop out to basically nothing for a few seconds at a time constantly.

If however, one MacPro is editing off the G-SPEED and a different MacPro starts to copy to/from a DroboPro, there’s no issue.

Any ideas? I’m leaning toward this being an Apple/OS issue but thought I’d throw this out here for possible comments.

Depends on how things are wired internally. From what you’ve said, it sounds like there may be some bus bottlenecking.

Is it possible to throttle down the bandwidth used by the G-SPEED?

We used to have similar issues with bus “choking” back in the SCSI-3 days. Contradictory to what you’d think, lowering the transfer rate of the SCSI device actually increased overall system performance/efficiency. The issue was the SCSI traffic would “clog the pipe” and cause a “one guy waiting on the other” situation rather than the ideal “two guys doing their own thing simultaneously” situation.

My 600MB/sec stat was just the maximum data throughput I can saturate the G-SPEED with in this config, with three MacPro edit client stations and the server itself all doing stuff to it. In real world use where this pops up, we’re probably using 50-100MB/sec total. Throw in a DroboPro copy operation and 150MB/sec absolute max.

Do you get different numbers connected Firewire 400 or USB? That would tell you if there’s some kind of contention between the Firewire and sharing.