Why is backup speed all over the place

[jmosk]

I am running Retrospect 10.5 on Windows 7. I recently upgraded to Windows 7 professional so I could increase my RAM space to 24Gb. Since the upgrade, my speed of backing up local disks writing to an external USB disk on the same machine (not a network backup), has dropped considerably. Backups which used to take 16 hours (with compare) have taken as much as 3 days !!! I can see periods when the backup is running at 1600 MB/min but most times I see it down to 16MB/min. Huge jumps in backup speed. At the 1600 MB/min it would take 16 hours to back up the 650Gb disk. But at that slow rate - several days. I look at the Task Monitor and it does appear that Retrospect is getting most of the Disk Activity. But I can see writes to the back up disk at 28MB/s at times, and 2MB/s at other times.

This hardware has not changed nor has the version of Retrospect. I don't see any other tasks running on the task monitor that might be taking away processing time from Retrospect. I thought perhaps Retrospect is just not getting CPU time which in turn would slow down its backup speed.

I am not sure where to look to try to locate this bottleneck that is causing backup speeds to vary to such a high degree. 3 days to do a full backup is unbearable.

[jmosk]

BTW - I increased the priority of the Retrospect task at a time the throughput was low. Using the task manager I increased the priority from Normal to Above Normal. It made no difference to the backup speed.

[Scillonian]

2 hours ago, jmosk said:

I am not sure where to look to try to locate this bottleneck that is causing backup speeds to vary to such a high degree.

To better try to find where the bottleneck may be you need need the extra functionality that is in the Task Manager in Windows 8.x and Windows 10. The feature available in Windows 8.x and Windows 10 that is of use here is the display of the percentage use of the system's individual resources. It is quite possible for a process to have a very low disk data throughput but be using 100% of the disk resources. This information is not visible in the Windows 7 Task Manager.

A search online for use windows 8 task manager in windows 7 will reveal some third party Windows 8.x style Task Manager alternatives for Window 7. Being a Windows 10 user now I have no personal current experience of these solutions for Windows 7 so provide this search information as is for a starting point.

[jmosk]

I found that resets of the system did not change what was happening. I was looking at what performance improvements I could make and increased the Virtual Memory size from that which was equal to my RAM size (24Gb) to the maximum recommended of 1.5 times the RAM size (36Gb). After doing this the backup speed seems to have stayed near the top speed and did not drop to one tenth of it at times. The backup that took 3 days ran in less than one day.

I have no idea why a change in the Virtual Memory size setting would have resulted in an improvement in the backup speed.

[Scillonian]

1 hour ago, jmosk said:

I have no idea why a change in the Virtual Memory size setting would have resulted in an improvement in the backup speed.

My suspicion is that with your original Virtual Memory setting, and Retrospect running, Windows was periodically deciding that some memory pages needed swapping between physical RAM and the pagefile more often than was desirable resulting in the erratic performance of Retrospect.