I was just attempting to help a client transfer files from an iMac to a new Windows computer (I didn't tell them to switch, they called me after buying the PC ).

Anyway, they had an average amount of data. About 20GB in docs, music, and other stuff, and about 200GB in photos. No big deal, I have some large flash drives. This is a mid-2011 iMac that they apparently never upgraded from Lion (so maybe that's the problem). It only has USB 2 ports. I'm using USB 3 flash drives.

The transfer speeds are SLOOOOOW. It was estimating 14GB of files taking 3 hours to finish. It took 800MB about 20 minutes. By my calculations, even with USB 2, 14GB of files should only take about 5 minutes.

Is it because the drives are FAT? Could the Mac just not like these particular drives? I haven't had problems on other PCs with these drives, and I'm not usually working on Macs. I'll admit they're just generic drives I picked up at the Micro Center checkout aisle. The branded ones.

I ended up having to take the whole iMac with me back to my place. I just got finished transferring 20GB to my Synology in about 5 minutes or less. Now I'll be exporting their iPhoto library and that should transfer pretty fast too. Still, would have been nice to not have to go back to the client a second time and get everything done in one visit.

Some googling gives me these possibilities:

- Spotlight is trying to index the external drive as you're using it. They say go into the privacy settings under Spotlight in System Preferences and add the external drives to the list of ignored drives.

- It may indeed be the FAT32 file system on those external drives. The problem is that you're transferring from Mac to PC, and that's the expected format that you'd use for that job since it's writeable and readable on both Mac and PC. NTFS would be faster but that's not writeable from the Mac. This article suggests using ExFAT, but this other page suggests that you should only use it if your external drive is a flash drive, or else it will also be slow.

... and of course, the possibility that the drives you purchased from the impulse-buy aisle at the store might not necessarily be top quality ...

Thanks, Tony. If I come across this issue on another Mac I'll remember this.

The drives are certainly inexpensive but they work at expected speeds on every PC I've tried them on.

Another behavior I forgot to mention was that much of the time, it appeared that the transfer would move some data, then pause, move data, then pause, etc. Nothing indicated this, just that the amount of data moved would show this behavior. Could be the Spotlight issue I guess...

Your note that the drives worked fine on a Windows machine but not on the Mac makes me think of other possibilities:

- Mac had problem with its USB port hardware, or the software drivers which drive the ports.

- The "Fat32 is slow" issue that I googled about might be mac-specific.

- The USB chipset hardware/firmware on the cheap drives was only tested against Windows machines and never got tested against Macs, or tested against macs with older operating systems, so you're running into an incompatibility between the drives and the Mac, or that specific Mac.

I have noticed that quite a few USB sticks receive "special" optimizations on MS-Windows for FAT/EXFAT/NTFS, often performing 2X-3X the speed when compared to the same formats on Linux. Not all though, and I tend to buy the ones that are as fast (or even faster) on Linux.

And how can I regognise which ones are fast and which ones are not Mark? Is that brand specific?

Mostly I just read the user-reviews, looking for people who have confirmed good performance with Linux. Otherwise, I purchase from places such as Costco who have very generous return policies.

One theory for the sticks with the "special" handling is that their firmware recognizes specific I/O sequences that MS-Win uses for FAT/NTFS and then implements some kind of internal optimizations for those "known" formats. Linux and MacOS will of course have different I/O sequences.

Cheers