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High CPU usage during backup

Posted: 29 Jul 2011, 14:54
by chcpnf
Hello,
we are using Firestreamer-RM under Windows Server 2003, running on a Pentium 4 at 3GHz. Our data are backed up on a network drive connected via iSCSI. During the backup, CPU usage is constantly near 100% and the throughput is rather poor. Process Explorer shows that the load is due to NRDVDSTR.sys and ntoskrnl.exe, hosted by the System process.
I tried switching off compression, but this did not significantly change the time needed for backup.
Is such a high CPU load considered normal? I realize that the hardware is quite ancient, but we are stuck with it for now.

Re: High CPU usage during backup

Posted: 29 Jul 2011, 20:04
by jsf
Make sure that both compression and encryption are disabled in Firestreamer-RM. If they are, then the high CPU usage is not normal. Try to back up to a local drive to see if the problem relates to the iSCSI drive.

Re: High CPU usage during backup

Posted: 01 Aug 2011, 11:27
by chcpnf
Thanks for your reply. I will try to narrow the problem down. Normal use, however, such as copying files to the iSCSI drive in explorer, does not seem to cause high CPU load.

Re: High CPU usage during backup

Posted: 01 Aug 2011, 19:58
by jsf
How big is your tape? Try copying a single file of the same size as your tape. Or better perform a backup to a local drive then copy the resulting tape to the iSCSI drive to see if there's a difference in the CPU usage.

Re: High CPU usage during backup

Posted: 02 Aug 2011, 13:02
by chcpnf
If by size of the tape you mean the size of the resulting backup file, this varies between 800GB and 1.2TB. This huge size also means I can't just perform the backup locally. For testing, I have copied 16GB to the iSCSI drive, both as one large file and a collection of small files. CPU use was around 10% for Explorer and System process combined during the copy operation.

Re: High CPU usage during backup

Posted: 02 Aug 2011, 21:18
by jsf
Does the CPU usage become high immediately after the backup started, or some time after?

Re: High CPU usage during backup

Posted: 03 Aug 2011, 10:19
by chcpnf
Thanks for your continued interest. We are running the large backup tasks over the weekend, so I will watch what happens on Friday and get back to you.

Re: High CPU usage during backup

Posted: 09 Aug 2011, 11:23
by chcpnf
OK, I logged into the server on Friday, half an our after the backup started. The backup file was already around 30GB and CPU usage was very low (around 10%). At this rate, the task should have completed in approximately 15h. However, on Monday, the backup task was still running, using the CPU at 100%.
So, the CPU usage indeed goes up at some later time. I also tried to run some performance logs to capture this in detail, but this failed somehow. Do you have a hunch what the problem with the backup might be?

Re: High CPU usage during backup

Posted: 09 Aug 2011, 20:41
by jsf
Check the kernel and user memory usage in Task Manager when the CPU usage is low and when it's high. Most likely, you have a memory leak. See Why does the amount of available memory rapidly decrease during a tape operation?

Re: High CPU usage during backup

Posted: 10 Aug 2011, 11:36
by chcpnf
Hmm, memory leak... But why would this cause excessive CPU load? And I didn't get the impression that the machine was under memory pressure as well, just maxing out the CPU.
I'll try to get the logs running during next weekend's backup.