Low write troughput on Adaptec 29160 (U160 SCSI)

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I have an Adaptec 29160 SCSI HBA (Ultra160 SCSI) sitting in a PCI 33/32 bus slot.

It has two Cheeatsh 15K.4 and one Cheetah 10K.6 connected on the LVD segment by a U320 SCSI cable.

All drives are working in U160 LVD mode.

The chipset is Intel i815, and the CPUs are two Pentium 3 Tualatin-S at 1400 MHz.

All drives are independent (no RAID).

The read STR speeds are excellent, and every drive's read STR corresponds to the STR measured by StorageReview in its initial review of that drive model.

The burst speeds (measured by HDTach 3.01) on Cheetahs 15K.4 are 113 MB/s, so it seems that the PCI bus has no performance issues (like it usually does on crappy VIA chipsets).

However, the write performance on any drive is rather bad. I can not acheve higher throughput than around 33-38 MB/s (I tested this by copying large files from one drive to another, etc.).

I used Seagate's SeaTools Enterprise to verify that all drives have Read and Write caching ON, and that they work in "Performance" (desktop oriented) caching mode.

Does anybody have any idea why is write throughput low, and how could I improve it? I would expect to be able to acheve around 55 MB/s (if the real troughput of the PCI bus is 110 MB/s).

P.S.: Don't nuke me because I value STR so much. I know everything about hard drive performance(s), and STR IS important for this setup, since I mostly move around LARGE files and do fast video montage (cutting & merging).

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Is there anybody who knows the solution to this issue?

I thought that, since this controller was very common, there must be people who have experienced the same.

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If your cache settings are all correct I would go into the MB BIOS increase the PCI Latency Timer to 64 or even 128, to see if that helps. Do you have a lot of PCI cards in the system? If so I would remove one PCI card at a time to see if any other PCI card is slowing down your disks.

Edited by hduser

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How are you testing the write through put?

I assume file copy? Or using ATTO or another similar tool?

If you're testing by copying files from 1 drive to another, remember that the data goes from the 1st drive to main memory, and then from memory to the 2nd disk. So you'll lost some write performance due to the reads taking place at the same time. (Since you mention Windows, due to using HDTach, Windows driver IIRC don't use the SCSI technique of being able to send data to 1 drive from another drive totally independent of the rest of the system - one of the huge benefits of SCSI is that it allows direct device to device communication, which IIRC Windows doesn't take advantage of).

My only suggestion to try to use a benchmark that writes to drive direct from memory, eg ATTO, dd (if using Linux/BSD/Solaris), etc.

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