Whoa, back up. You're telling me it's going to take that long to back up?

September 9, 2011 11:11 AM

12 hours to copy 96GB. Is that right?

I'm manually backing up my Aperture library from one USB 2.0 drive to another but OSX (Snow Leopard) is telling me it will take 12-16 hours to complete.

I smell a rat. I've checked both disks with Disk Utility and both appear to be okay.

Shouldn't the transfer be much quicker? What do think might be wrong?

posted by run"monty to computers & internet (15 answers total)

you might check the cable between them. i have a cable that if i try to transfer anything over it, it takes way longer than normal.
posted by nadawi at 11:14 AM on September 9, 2011

What are the hard drives themselves, SATA or IDE?
posted by rhizome at 11:14 AM on September 9, 2011

Which file format are both drives? HFS+ ? I've found NTFS transfers to be quite slow through the free Macfuse NTFS driver.
posted by sharkfu at 11:15 AM on September 9, 2011

If you're talking about two external drives over USB 2.0, yes, my experience is that it is very slow. It's much faster when one of the drives is internal and thus running off of the SATA connectino.
posted by Admiral Haddock at 11:15 AM on September 9, 2011 [1 favorite]

In my experience with USB disks that doesn't sound insane.

Running the numbers suggests that at least one of the disks is running at USB 1.0 transfer rate (up to 12Mbps) instead of USB 2.0 (up to 480Mbps):

96*1000*8/480/60 = ~27 minutes at USB 2.0
96*1000*8/12/60/60 = ~18 hours at USB 1.0

I normally just leave transfers like that running overnight.
posted by katrielalex at 11:17 AM on September 9, 2011

12 hours for 96GB is roughly 2.2MB/sec and really freakin slow. I'd check for a bad cable.

Alternative: Is it possible to do this in two steps? Transfer to the internal hard drive, then transfer on to the second hard drive.
posted by Mister Fabulous at 11:19 AM on September 9, 2011

I regularly copy 120 GB and it takes 90 minutes over USB 2.0. It is a series of large files though. It you have 10s of thousands of files it make take longer due to OS file management details. Still it sounds too long.
posted by bottlebrushtree at 11:20 AM on September 9, 2011

You can't use the theoretical limit of USB 2.0 (480mbps) to calculate how long something like this should take - real world USB speeds are typically much, much MUCH slower.
posted by The Lamplighter at 11:25 AM on September 9, 2011 [2 favorites]

Well I tried different cables but the same thing happened.

Left it running for five minutes or so... OSX now reporting a more sensible time.

Looks like I panicked too soon. (We're talking about a years worth of family photos that, until half an hour ago, I thought I'd lost -- hence the sudden urge to back everything up).

For the record: All drives are HFS+. One is IDE the other SATA.
posted by run"monty at 11:32 AM on September 9, 2011

I was going to say to do what you did. It sometimes takes a while for the OS to really calculate how long something like this will take, and leaving it running for even a few minutes can end up showing a greatly reduced time.
posted by OmieWise at 11:42 AM on September 9, 2011

From what I understand, if software developers were to devote enough resources to accurately estimate the time remaining, then the estimation process itself would slow everything down by a pretty large amount. Those dialogs are pretty much rough guesses.
posted by Devils Rancher at 11:42 AM on September 9, 2011

My experience is that OSX time estimators are initially quite wrong.
posted by Xurando at 11:49 AM on September 9, 2011

Google is nice for calculating these things: 96GB / 24 hours = 2.27MBps
A realistic USB copy speed is maybe 20MBps: 96GB / 20MBps = 1.3 hours

So yeah, 24 hours = broken :) Unless it's TONS of really really tiny files. Could happen I think.

But yeah, you can get an estimate of the actual file transfer speed by opening /Applications/Utilities/Activity Monitor.app, and going to the Disk Activity tab thing at the bottom. It shows the transfer rate over the last second or two. Keep an eye on that for a while and you'll see the actual transfer rate. (Which you can then plug into the Google search calculator to get a decent time estimate ...)
posted by krilli at 12:31 PM on September 9, 2011 [1 favorite]

Make sure your real time virus check is disabled.
posted by mygoditsbob at 7:23 PM on September 9, 2011 [1 favorite]

"Make sure your real time virus check is disabled."

On OS X? Surely you jest.

The time doesn't seem unreasonable, especially when you consider the word that nobody else seemed to look at: Aperture. Your Aperture library is a collection of thumbnails, metadata, master photographs, and lots of other files, and when you copy all those things, OS X seems to over estimate the time it will take to copy. Once you get past the smaller files, I bet the time will drop dramatically. An initial estimate of 12 hours will likely be 6 or less. My Aperture library is 250GB, and it takes many hours to copy, even over FireWire 800.

But if it's data you feel is important, copy/paste it, and do a differential copy onto the same directory with rsync, to make sure everything is there. Or just use Aperture's built in Vault feature and back up to an external disk.
posted by santaliqueur at 8:55 PM on September 9, 2011