Date: Sun, 11 Apr 1999 19:14:25 -0400 (EDT) From: Andrew Gallatin <gallatin@cs.duke.edu> To: freebsd-scsi@freebsd.org Subject: odd performance 'bug' & other questions Message-ID: <14097.8430.806061.277769@grasshopper.cs.duke.edu>
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We're setting up a few large servers, each with 6 9GB seagate medalist pro drives spread across 2 scsi controllers (aic7890 & ncr53c875). We've noticed that if we set up the disks using a simple ccd stripe, after trying various interleaves, the best read bandwidth we can get is only ~35-40MB/sec (using dd if=/dev/rccd0 of=/dev/null bs=64k), which is odd because we'd thought we should be getting at least 55-60MB/sec, as we get about 13.5MB/sec from each drive with the same test. Upon closer examination, we discovered that on some of the drives the performance wanders all over the place -- if you do a dd if=/dev/rX of=/dev/null bs=64k on an individual disk on an otherwise idle system & watch with iostat or systat, you can see the bandwidth jump around quite a bit. I'm thinking that my performance problems might be due to the fact that the reads aren't really sequential, rather the disk arm is moving all over the place to read remapped defective blocks. Using camcontrol to look at the defects list on some of these drives, I see that its HUGE. I've seen one disk with over 1100 entries in the primary defects list. Should I be alarmed at the size of the defects list? Should I complain to my vendor, or is this typical? Also, the ncr controller fails to give me a defects list, I assume this is a bug in the driver? (I'm running -current, dated this Thurs). camcontrol complains: error reading defect list: Input/output error, and I see this on console: (pass3:ncr0:0:0:0): extraneous data discarded. (pass3:ncr0:0:0:0): COMMAND FAILED (9 0) @0xc39a3600. Thanks for your help, ------------------------------------------------------------------------------ Andrew Gallatin, Sr Systems Programmer http://www.cs.duke.edu/~gallatin Duke University Email: gallatin@cs.duke.edu Department of Computer Science Phone: (919) 660-6590 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-scsi" in the body of the message
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