High CPU usage during backup

The technical support forum for Firestreamer-RM 2.x (the virtual tape drive for NTBackup).
chcpnf
Posts: 11
Joined: 29 Jul 2011, 14:21

High CPU usage during backup

Post by chcpnf » 29 Jul 2011, 14:54

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.

jsf
Cristalink Support
Posts: 300
Joined: 29 Aug 2010, 09:03

Re: High CPU usage during backup

Post by jsf » 29 Jul 2011, 20:04

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.
Best regards,
John Smith
Cristalink Support

chcpnf
Posts: 11
Joined: 29 Jul 2011, 14:21

Re: High CPU usage during backup

Post by chcpnf » 01 Aug 2011, 11:27

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.

jsf
Cristalink Support
Posts: 300
Joined: 29 Aug 2010, 09:03

Re: High CPU usage during backup

Post by jsf » 01 Aug 2011, 19:58

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.
Best regards,
John Smith
Cristalink Support

chcpnf
Posts: 11
Joined: 29 Jul 2011, 14:21

Re: High CPU usage during backup

Post by chcpnf » 02 Aug 2011, 13:02

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.

jsf
Cristalink Support
Posts: 300
Joined: 29 Aug 2010, 09:03

Re: High CPU usage during backup

Post by jsf » 02 Aug 2011, 21:18

Does the CPU usage become high immediately after the backup started, or some time after?
Best regards,
John Smith
Cristalink Support

chcpnf
Posts: 11
Joined: 29 Jul 2011, 14:21

Re: High CPU usage during backup

Post by chcpnf » 03 Aug 2011, 10:19

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.

chcpnf
Posts: 11
Joined: 29 Jul 2011, 14:21

Re: High CPU usage during backup

Post by chcpnf » 09 Aug 2011, 11:23

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?

jsf
Cristalink Support
Posts: 300
Joined: 29 Aug 2010, 09:03

Re: High CPU usage during backup

Post by jsf » 09 Aug 2011, 20:41

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?
Best regards,
John Smith
Cristalink Support

chcpnf
Posts: 11
Joined: 29 Jul 2011, 14:21

Re: High CPU usage during backup

Post by chcpnf » 10 Aug 2011, 11:36

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.

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