Disk-To-Disk-To-Tape backups

[ochadd]

We do about 300GB of data backup every night. My current setup uses Brightstor ArcServ(now CA ArcServ) using two seperate jobs. The first job backs up all the servers onto a consumer level external USB 1TB drive attached to one server starting at 11pm. The second job then backs up that external drive to tape without compression to be taken offsite at 6:30am.

The backups, both the read and write operation, scream along at 8.5MBps even though the drive benchmarks out at 29MBps. I'm not sure if it's a compatibility issue with the USB drive and the software but when I back up to the SCSI RAID array it finishes in a fraction of the time. I am barely able to finish the backup to tape in an 8 hour day.

I've reinstalled the software, tested backing up to local disk, tried multiplexing the job, and everything is pointing to issues dealing with the USB drive. Anyone have a suggestion on how to speed this up using my current setup? Suggestions for some inexpensive, relatively fast, external SCSI storage?

 

[MerlinRML]

Originally posted by: ochadd
I've reinstalled the software, tested backing up to local disk, tried multiplexing the job, and everything is pointing to issues dealing with the USB drive. Anyone have a suggestion on how to speed this up using my current setup? Suggestions for some inexpensive, relatively fast, external SCSI storage?

USB is slow. That would have been my guess, and it sounds like you've proven that the problem is in your storage system. I'm not sure why you're making the leap from USB to SCSI/SAS without considering SATA/eSATA first, though. You went from one of the slowest options to one of the fastest without stopping anywhere in the middle.

I would bet that a single SATA/eSATA hard drive would probably improve your performance quite a bit. My own approach would be to try to identify your theoretical maximum based on the next biggest bottleneck (usually the speed of your network or the backup client's ability to send data) and start evaluating storage systems that should be able to meet that level of performance.

 

[ochadd]

I don't believe the speed of the USB drive is the issue. Benchmarking the drive using HDtune and Atto reports 28-29MBps transfers which would be plenty fast. The problem seems to be in the way ARCserv is handling the transfers. Doing transfers from the USB drive to the local disk and then back again I get 292MB copied in 7-10 seconds flat = 29+MBps which is the USB interface being capped out. Both read and write operations are working at theoretical max for USB 2.0 and the device. This is using a stop watch and a drag and drop copy.

The tape drive I'm using maxes out at around 500MB/min or 8MBps, oddly about the same speeds I'm getting going from the local RAID array to the USB drive on a completely seperate job.

Windows built in backup utility won't detect the tape drive as a device for whatever reason so I've been unable to try different software to see if it is ARCserv for sure causing the issue. I'm guessing the software somehow marks the drive as off-limits to other applications. Even with all the ARCserv "engines"/service stopped windows backup won't detect it.

 

[ochadd]

Using Windows backup utility I was able to get 16-25MBps running a test backup four times back to back. ARCserv seems to have an issue writing to my USB device.