Slow TAR but not CPIO

[eepico]

Dear all,

I've just upgraded my SCO Openserver from 5.0.2 to 5.0.6 and hardwares also. I found that the tar backup or restore was extremely slower than my old system. It took me more than 4 times time to finish backup a similar amount of data. But when I used CPIO instead, it was very fast to complete than my old system. I'm using a new DDS-4 tape drive and RAID-1 disk mirrors. My old box didn't have any RAID and the tape drive I guess was DDS-3.

Any hints why tar suddenly being slower after hardware and software changes? Any configuration file I need to change in sco or tar?

Jack

 

[apeasecpc]

I am thinking the difference between tar and cpio is some kind of buffering that the OS does differently for the two commands. Can you tell if the tape drive is able to run pretty much straight through or if it is doing a lot of seeking when you use tar?

Is your tape drive on the same controller as your hard drive? If it is you should consider moving it because the speed difference between hard drive and tape devices can effect performance if they are both on the same scsi bus.

You should also look at the controller settings for the tape drive scsi ID. Sometimes tape drives work more efficiently (i.e. faster) if you reduce the controller speed setting for that ID.

 

[eepico]

Can you tell if the tape drive is able to run pretty much straight through or if it is doing a lot of seeking when you use tar?
Ans: It reads the file block very slowly when using TAR, especially large file; CPIO is smooth!!

Is your tape drive on the same controller as your hard drive? If it is you should consider moving it because the speed difference between hard drive and tape devices can effect performance if they are both on the same scsi bus.
Ans: No, the tape drive is on the scsi card and the harddisk is on the RAID card, they are on different controllers, ad160 & ciss.

You should also look at the controller settings for the tape drive scsi ID. Sometimes tape drives work more efficiently (i.e. faster) if you reduce the controller speed setting for that ID
Ans: Yes, thanks. I will try to change it, but why CPIO not affected in this case?

 

[apeasecpc]

I honestly don't know why tar is slow yet cpio is not. I use backupedge so I've never done anything with cpio, and I only used tar for a short time before I got the backupedge software working.

I just recently upgraded from 5.0.0 to 5.0.6 myself, and I haven't experienced any slow down problem, but I didn't actually make any changes to the hardware. My tape backups take about the same amount of time as before the upgrade.

If it wasn't for the fact that cpio is working fine I would think that slowdown is related to the controller being set too fast for the drive. The cpio program must be doing some kind of buffering of the data which allows it to write in a continuous stream instead of stop and go for each file. That's the only thing I can think of at this point.