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SubjectRe: Strange disk-write speeds
On Fri, 15 Feb 2002, Helge Hafting wrote:

> "Richard B. Johnson" wrote:
> >
> > Weird. I have two identical SCSI drives. They both synchronize
> > at 40 Mb/s on my Buslogic controller. They are the two ...
> > Vendor: SEAGATE Model: ST318233LWV Rev: 0002
> > ... drives shown below.
> >
> > They both have ext2 file-systems occupying a single partition.
> > The time to write a file that fills up the file-system on the
> > "Id: 01" drive is about 1/2 an hour and the time to write a
> > file that fills up the file-system on "Id: 02" is about 1/2 day!
> >
> > This is with the file created with "O_SYNC". If the file is
> > not created with "O_SYNC", there is no apparent difference in
> > write speed.
> >
> > If I swap the jumpers on the two drives to isolate the drives
> > from the problem, the slooooo drive is the logical "ID: 02",
> > always... not the physical one!
> >
>
> O_SYNC writes takes different time depending on the scsi ID?
>
> _Very_ strange, unless your /etc/fstab looks different for
> /dev/sdbX and /dev/sdcX
> I.e. different mount options that indeed depend on scsi id.
> Also check to make sure nothing else is running and accessing
> any partition on sdc, that might force those sync writes
> to seek more. (I guess the slow disk is noisy?)
>
> Helge Hafting
>

Well here are the buslogic statistics.

The faster drive completed more transactions for the same amount of
data written. This means that the faster drive used smaller buffers.
But, its not the drive that's faster, it's the logical order of
the drive. Maybe the SCSI command queue starts at the first drive
every time, rather than the next drive?? "Next" being one after the
previous access. So, the third drive doesn't have the resources that
the second one had, and the first one has all the resources of the
previously-completed commands.


***** BusLogic SCSI Driver Version 2.1.15 of 17 August 1998 *****
Copyright 1995-1998 by Leonard N. Zubkoff <lnz@dandelion.com>
Configuring BusLogic Model BT-958 PCI Wide Ultra SCSI Host Adapter
Firmware Version: 5.06J, I/O Address: 0xB400, IRQ Channel: 11/Level
PCI Bus: 0, Device: 12, Address: 0xDF000000, Host Adapter SCSI ID: 7
Parity Checking: Enabled, Extended Translation: Enabled
Synchronous Negotiation: UUUUUUF#UUUUUUUU, Wide Negotiation: Enabled
Disconnect/Reconnect: Enabled, Tagged Queuing: Enabled
Scatter/Gather Limit: 128 of 8192 segments, Mailboxes: 211
Driver Queue Depth: 211, Host Adapter Queue Depth: 192
Tagged Queue Depth: Automatic, Untagged Queue Depth: 3
Error Recovery Strategy: Default, SCSI Bus Reset: Enabled
SCSI Bus Termination: High Enabled, SCAM: Disabled
*** BusLogic BT-958 Initialized Successfully ***

Target 0: Queue Depth 28, Wide Synchronous at 40.0 MB/sec, offset 15
Target 1: Queue Depth 28, Wide Synchronous at 40.0 MB/sec, offset 15
Target 2: Queue Depth 28, Wide Synchronous at 40.0 MB/sec, offset 15
Target 4: Queue Depth 3, Synchronous at 10.0 MB/sec, offset 15

Current Driver Queue Depth: 211
Currently Allocated CCBs: 91


DATA TRANSFER STATISTICS

Target Tagged Queuing Queue Depth Active Attempted Completed
====== ============== =========== ====== ========= =========
0 Active 28 0 190452 190452
1 Active 28 0 2299708 2299708
2 Active 28 0 517521 517521
4 Not Supported 3 0 22140 22140

Target Read Commands Write Commands Total Bytes Read Total Bytes Written
====== ============= ============== =================== ===================
0 91569 98874 1526159872 5036346880
1 76628 2223071 8503424 75675684864
2 13033 2104479 794752 74215583232
4 10 21789 20480 713973760

Target Command 0-1KB 1-2KB 2-4KB 4-8KB 8-16KB
====== ======= ========= ========= ========= ========= =========
0 Read 27517 5195 5072 6402 3980
0 Write 1765 820 315 25194 2302
1 Read 0 2 0 48658 5550
1 Write 0 0 0 1430296 88987
2 Read 0 5 0 3837 531
2 Write 0 0 0 1308773 10785
4 Read 0 0 10 0 0
4 Write 0 0 0 0 0

Target Command 16-32KB 32-64KB 64-128KB 128-256KB 256KB+
====== ======= ========= ========= ========= ========= =========
0 Read 2801 40254 221 127 0
0 Write 831 3848 62437 130 1232
1 Read 7713 7058 1907 5740 0
1 Write 7855 16713 623979 1624 53617
2 Read 89 8571 0 0 0
2 Write 7776 9892 142436 1097 23720
4 Read 0 0 0 0 0
4 Write 1 21788 0 0 0


ERROR RECOVERY STATISTICS

Command Aborts Bus Device Resets Host Adapter Resets
Target Requested Completed Requested Completed Requested Completed
ID \\\\ Attempted //// \\\\ Attempted //// \\\\ Attempted ////
====== ===== ===== ===== ===== ===== ===== ===== ===== =====
0 0 0 0 0 0 0 0 0 0
1 0 0 0 0 0 0 0 0 0
2 0 0 0 0 0 0 0 0 0
4 0 0 0 0 0 0 0 0 0

External Host Adapter Resets: 0
Host Adapter Internal Errors: 0



Cheers,
Dick Johnson

Penguin : Linux version 2.4.1 on an i686 machine (797.90 BogoMips).

I was going to compile a list of innovations that could be
attributed to Microsoft. Once I realized that Ctrl-Alt-Del
was handled in the BIOS, I found that there aren't any.


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