Two disk drives attached to the same SCSI interface card on RX4640

[CAS_2]

Hi.

Due to some performance problems in a rx4640 IA64 server, I discovered that both disks in VG00 attached to the same SCSI interface card:

Class I H/W Path Driver S/W State H/W Type Description
============================================================================
disk 0 0/0/3/0.0.0.0 sdisk CLAIMED DEVICE TEAC DV-28E-B
disk 1 0/1/1/0.0.0 sdisk CLAIMED DEVICE HP 36.4GST336753LC
disk 2 0/1/1/0.1.0 sdisk CLAIMED DEVICE HP 36.4GST336753LC

In the other hand I found two SCSI interface cards:

ext_bus 2 0/1/1/0 c8xx CLAIMED INTERFACE SCSI C1010 Ultra160 Wide LVD A6829-60101
ext_bus 3 0/1/1/1 c8xx CLAIMED INTERFACE SCSI C1010 Ultra160 Wide LVD A6829-60101

First, I thought HP staff didn't configure properly this server and they inserted both disks in two slots attached to the same If Card -- I guessed this server had 4 slots for disks as L-class server had.
Due that I cannot see the box, I downloaded Rx4640 operations manual from HP doc site and saw that ONLY two internal disks are possible.

Then, Why both disks are attached to the same SCSI interface card and other one has no device attached ?

[Torsten. · Accepted solution]

While ordering the system, you can order it with or without the dual bus (duplex) option.

The default is a single bus configuration, so both disks are on only one bus.

Same for rp4440.

If in simplex mode, you may use the upper of the 2 external connectors. In duplex mode non of the external connectors is supported.

[timmy b.]

CAS,

Torsten is (as usual!) correct. You need to have the duplex option to put your drives on individual busses. Here is the link to the installation manual, look to page 61 or so for the Duplex board instructions. This manual is VERY handy, with a lot of good information.

http://tinyurl.com/cyrh8

Good Luck - Tim

[Zygmunt Krawczyk]

To convert from simplex to duplex SCSI you need to buy duplex PCA backplane A9740B

[rick jones]

And, with the "how to get the two internal discs on separate SCSI busses" question addressed, what sort of performance problem were you having and what leads you to suspect the issue is with having both discs on the same SCSI bus?

[Torsten.]

@timmy: Thank you! ;-))

Regarding Ricks posting: Do you have any problem with this configuration? Even you have the duplex config, there are still SPOFs like the I/O card and the slot.
No reason to be worry about the config.
A single server isn't a high availability environment, but your current performance should be good enough.

[CAS_2]

My box is running out of memory.

I found high CPU time percentages for %wio in 'sar -u' output.

I ran 'sar -d' and fount first physical volume of vg00 is near 100% busy (second one is just 20%). Busy percentages on application disks are fine.

"swapinfo -tam" output shows dirty swap.

Then I used "vmstat" to figure out if box was paging.... yes it was.

The outcome of adding the sizes of all shared memory segments is 7.5 GB but physical memory size is 6GB.

The issue of this thread was a side effect

[rick jones]

While splitting the mechs across two SCSI busses may help a little, I suspect that the percentage utilization of the mech was more on I/O's per second rather than bus bandwidth - unless I missed where the sar data said that the bandwidth consumed was somewhere near Ultra160 limits.

Anyway I guess you already know to get more RAM right?-) Meanwhile, depending on your workloads, you might be able to finesse things a bit by dropping dbc_max_pct to make sure that buffer cache isn't getting in the way.

[CAS_2]

thank you, guys