Slow access to backup file

[pi314]

I am using Retrospect Pro 6.5 on WinXP. I am backing up to an external USB2 drive. I just backed up for the first time yesterday, the total backup file size came to about 50GB.

 

When I tried a subsequent incremental backup, Retrospect sat there for about an hour accessing the external drive before starting the backup. I used the file monitor tool to see what Retrospect was doing and it was reading the entire 50GB file from beginning to end and during this time, Retrospect was completely unresponsive.

 

This does not seem like normal behaviour to me. Why is Retrospect reading through the entire backup file just to do an incremental backup?

 

- Paul

[awnews]

I haven't seen RP doing what you're describing, and I do some backups to USB2 drives.

 

You mention that it's a USB2 drive. Are you sure it's plugged into a USB2 (rather than USB1) port on your PC?

 

You could try doing Disk Backups (a bunch of little files) rather than File Backups (one big file). This works in RP6.5 but it's easier in RP7 (the former wanted to save at the root of the drive unless you manually fiddled with the Backup Set settings). And the grooming feature of R7 is handy for keeping the backup sizes (# of backups) under control. There's a free R7 trial and you can revert to R6 if you don't like it (suggest you start a new R7 backup set for any testing).

[pi314]

Quote:

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You mention that it's a USB2 drive. Are you sure it's plugged into a USB2 (rather than USB1) port on your PC?

 

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Yes, I'm sure it's USB2, because the read/write speed of the disk is going at about 10MB/s which is well beyond USB1.

[cajun100]

Hmmm, with a USB2 conenction you should be getting somewhere between 200 and 400MB/s direct transfer from PC hard disk to USB hard disk. I think you are getting a USB1.0 response (if you are seeing 10 MB/s transfer rate) ... either because of the direct PC port connection, the hub you are using, other devices maybe plugged into the hub, etc.

I would double-check which ports have which USB devices connected. This is a common mistake made by almost everyone. I have done it myself, more than once.

[awnews]

Just to make sure we're all using the same terminology, "MB/s" is often used for "MegaBytes/second" while "Mb/s" is often used for "Megabits/second." USB2 can provide 200 and 400Mbits/s, not MBytes/sec.

 

The theoretical (you'll never see it) bit rate for USB2 is 480Mbits/sec. The theoretical (again, you'll never see it) USB1 transfer tate is 12Mbits/sec (*originally* USB1 was 1.5Mbits/s). So pi314 would be seeing an amazingly good USB1 rate or a lousy USB2 rate depending on bits vs. bytes. In practice both of these I/Fs tend to provide under half of the rated speed.

[cajun100]

LOL, you are right, the terminology is important!!!!!

Well, I should have used that small "b" after the big "M". This is as bad as the broadband speed discussions!!! I must be drive-spec happy.

Still seems like our friend above is within the USB 1 envelope, though, or a disfunctional USB 2 connection?

For a while on one of my machines I had some conflicts between Firewire and USB ports -- on a PCI add-in board -- could never run the two at the same time. My latest add-in, a front panel thing, is much better, and performance is very nice (I see near 400 "Mbps" in Retrospect under USB from time to time, mostly about 280 or so on average, with a large partitiion transfer.

[pi314]

The maximum speed for USB1.1 is 1.5MB(megabytes)/s or 12Mbits/s. The maximum speed for USB2 is 60MB(megabits)/s or 480Mbits/s. Typical harddrives can only read/write at about 20MB/s or so. So the connection definitely USB2, and 10MB(megabytes)/s is not unreasonable for an external USB2 harddrive.

 

However, we have strayed from the path here. The problem isn't related to USB1 vs USB2. It's that Retrospect is scanning the entire backup file without necessity before starting the actual backup and blocking the GUI while doing it. Anyone have any ideas as to what might be going on.

 

- pi