Performance problems:Did PE2850 ship with SCSI-2 backplane?

J. Epperson Dell at epperson.homelinux.net
Tue Sep 6 08:59:18 CDT 2011


On Tue, September 6, 2011 08:26, Brent Kimberley wrote:
> Hi,
>
> I have a question for the group.  Does anyone know if PE2850 servers were
>  shipped with a SCSI-2 backplane?
>
> This PE2850 was shipped from with the following options: a)  N7108
> (Module, Information, Backplane 1X6, P2850); AND, b) T8677 (Assembly,
> Cable, Scsi, Backplane Riser, CHANNEL A...)
>
> I believe the machine has been crippled by a SCSI-2 backplane.
>
> If true, can anyone advise a simple way to work-around the issue?
> Perhaps jumper settings, cables, etc.?
>
> Has this happened to anyone else?
>
> Observations: - The system has been undergoing a slow/prolonged
> end-of-life failure for several years - The backplane reports SCSI-2 (i.e.
> 10MB/sec) - performance does not and did-not meet expectations * system
> yields 1 to 4 MB/sec for bulk sequential reads (i.e. dd bs=4MB
> if=/dev/<raw-SCSI-320-disk-array> of=/dev/null count=1000) * System
> should yield 40 to 240 MB/sec for bulk sequential reads * System performs
> worse during random access reads - system has low throughput / high
> latency (system should have high throughput / low latency as it was
> professionally configured & contains only OEM, enterprise, Ultra SCSI 320
> components) - unable to backup or archive in a timely fashion - system
> barely meets minimum "sunny-day" expectations when running contiguously
> for 8 to 18 hours per day.
>

Not normal.  Here's a similar machine (although with a PERC):

[root at utility etc]# dmidecode|grep -i poweredge;lspci|grep RAID;dmesg|grep
-i  model ;fdisk -l;dd bs=4MB if=/dev/sda3 of=/dev/null count=1000
        Product Name: PowerEdge 2850
02:0e.0 RAID bus controller: Dell PowerEdge Expandable RAID controller 4
(rev 06)
  Vendor: PE/PV     Model: 1x6 SCSI BP       Rev: 1.0
  Vendor: MegaRAID  Model: LD 0 RAID5  419G  Rev: 521X

Disk /dev/sda: 440.0 GB, 440087347200 bytes
255 heads, 63 sectors/track, 53504 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1               1           4       32098+  de  Dell Utility
/dev/sda2   *           5          69      522112+  83  Linux
/dev/sda3              70        1101     8289540   82  Linux swap / Solaris
/dev/sda4            1102       53504   420927097+   f  W95 Ext'd (LBA)
/dev/sda5            1102        8908    62709696   8e  Linux LVM
/dev/sda6            8909       53504   358217338+  83  Linux
1000+0 records in
1000+0 records out
4000000000 bytes (4.0 GB) copied, 30.6845 seconds, 130 MB/s





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