Promise PDC20267 ATA RAID, poor write performance

Frode Nordahl frode at nordahl.net
Mon Sep 13 02:24:20 PDT 2004


On Sep 11, 2004, at 12:49, Søren Schmidt wrote:
> OK I got this this setup now:
>
> atapci0: <Promise PDC20267 UDMA100 controller> port 
> 0xb000-0xb03f,0xb400-0xb403,0xb800-0xb807,0xd000-0xd003,0xd400-0xd407 
> mem 0xfd000000-0xfd01ffff irq 16 at device 3.0 on pci0
> ad1: 14305MB <Maxtor 2R015H1/EAH41MF0> [29065/16/63] at ata2-master 
> UDMA100
> ad2: 14305MB <Maxtor 2R015H1/EAH41MF0> [29065/16/63] at ata3-master 
> UDMA100
> ar0: 14305MB <ATA RAID1 array> [1823/255/63] status: READY subdisks:
>
> Controller the same, disks are an earlier verision of those "low 
> profile" Maxtor disks, just somewhat slover than yours.
>
> pizzabox# dd if=/dev/zero of=fill bs=1m count=2000
> 2000+0 records in
> 2000+0 records out
> 2097152000 bytes transferred in 122.908771 secs (17062672 bytes/sec)

I have done some more test now, reseated cables, disabling other IDE 
controllers etc. to no avail. I have tested both drives against the 
ICH2 controller with very good results.

After some fooling around I found the following:
ar0: ATA RAID1 subdisks: ad4 ad6 status: READY
# dd if=/dev/zero of=fill bs=1m count=100
100+0 records in
100+0 records out
104857600 bytes transferred in 29.298259 secs (3578970 bytes/sec)
# atacontrol detach ata2
# dd if=/dev/zero of=fill bs=1m count=100
100+0 records in
100+0 records out
104857600 bytes transferred in 3.080246 secs (34041957 bytes/sec)

(this also works when writing 2GB...)

That is, whenever I run with a single disk or a degraded RAID transfer 
speeds are ok. I have tried this both ways, so it is not one of the 
disks / cables that is broken. As soon as I rebuild the RAID again, 
write speeds drop to 3MB/s.

Any ideas as of how to debug this?

Mvh,
Frode

> -Søren
>



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