I have an iOmega eGo 320GB portable drive connected through USB2.0 to my laptop running Windows Vista. It's been working fine for quite some time until recently it became very slow when writing e.g. when copying ~300MB movie over to the drive at first it is extremely fast but it actually doesn't write it only puts in cache and then hangs on last 10-20MBs for about a minute. When copying larger files it's the same story: starts fast but then slows down to ~5MB/s (sometimes even slower down to 2MB/s). Strange thing is that I have always had caching disabled for this drive (it was disabled by default and I never bothered changing it).
At first I thought that the disk is dying so I checked S.M.A.R.T. values and everything is fine there. I also run chkdsk and it seemed to fix the problem - it worked fast for a few minutes but then it slowed down again. I also tried plugging it into another USB port - no difference.
Additionally I noticed that reading under certain circumstances is sometimes slower e.g. loading times for some games are ~10 times longer, whereas simple copying files from this drive to my internal HDD is fast.
I ran a speed benchmark using CrystalDiskMark with a 5x100MB run and strangely got these results:
read write (MB/s) Seq 33.05 28.25 512k 17.30 15.27 4k 0.267 0.372 4kQD32 0.510 0.260
This is different from what most other people have (I've found many threads about slow disk write while googling but all of them were slow on benchmarks too) which is why I decided to post this problem here.
BTW most of the time when writing (or sometimes reading) the activity led is mostly idle (blinks a while and then stops for longer, sometimes has slower blinks ~1 sek, sometimes goes off for a few seconds - extremely long blink :) ) but when benchmarking, defragmenting or just reading (copying from this drive, installing apps from installers there, watching HD videos) it is blinking really fast (like it should) and there are no slowdowns.
It shouldn't be driver issue unless stock Windows drivers have some issues I'm not aware of.