topic Re: LVD/SCSI Throughput in Disk

LVD/SCSI Throughput

Harvindar Singh — Thu, 02 Oct 2003 01:57:15 GMT

I have a N-class and its LVD/SCSI connector (on the I/O Connector Panel) has 2 devices connected: a DVD reader and DDS tape drive.
The "Diffsens" LED is off, indicating that throughput is that for SE devices (5-10 MB/sec). This is as it should be.
For our DR purposes, I have to connect up a JBOD (vendor is Nexsan) to copy both the applications and a large image repository (500GB) off the N-class. Note that the JBOD is the only device on the SCSI chain,ie, both SE devices (DDS and DVD) are disconnected. The JBOD is then connected to a N-class at our DR site; this is to speed up the time for the apps to be available should a disaster occur; I do this every couple of months.
I tried the copy for the first time recently and got a throughput of 2.5GB/hour which indicates that the LVD connector was in SE mode. Being new to HP, I did not notice the LED before today unfortunately. I need to find out if the throughput is automagically set based on the devices connected or whether it can be configured or something else.
Thanks for the help.

Re: LVD/SCSI Throughput

Leif Halvarsson_2 — Thu, 02 Oct 2003 03:12:58 GMT

Hi,

There must be more problems then if working in SE or LVD mode. 2.5 GB/hour is 0.7 MB/s, only a fraction of SE speed.

You should not need to to any configurations with the SCSI bus. The bus switches to SE mode if connecting a SE device and returns to LVD mode if disconnecting the device.

Re: LVD/SCSI Throughput

Alexander M. Ermes — Thu, 02 Oct 2003 03:21:10 GMT

Hi there.
Try to avoid connecting different kinds of SCSI to the same bus.
If you connect a LVD device and a SE device to the same bus, the throughput will be down to 5 MB/sec in worst case.
The bus will automatically be set to the slowest device.
This is the reason, why i put a separate SCSI interface into my pc for my scanner.
The disks run on LVD, cdrom, burner, dvd, tape run on SE scsi of a TEKRAM U2W interface.
Rgds
Alexander M. Ermes

Re: LVD/SCSI Throughput

Joshua Scott — Thu, 02 Oct 2003 10:42:48 GMT

As was mentioned, there must be other issues if the speed is only 2.5GB/h. I would expect 18 GB/h on a SE bus. However, the Ultra2 LVD port on the N-class server should get you 288GB/h. Make sure you are using an LVD terminator & a cable that can handle LVD. also, what length is the cable?

-Josh

Re: LVD/SCSI Throughput

Harvindar Singh — Thu, 02 Oct 2003 17:34:20 GMT

This is to help clarify the problem based on the responses so far.
There are no other devices on the hardware path "0/0/1/0" when the JBOD is connected; both DDS and DVD reader are disconnected.
I checked the root volume group and the 2 disks there are off the hardware path "0/0/2/*".
Since there are no other devices on the SCSI chain, it should automagically have LVD throughput rates.
I am using a LVD terminator on the JBOD; it has a lable on it "LVD/SE Active Switchable Terminator" and is from HP. The JBOD has got auto-terminated LVD connectors but I have not tried these yet.
The LVD cable I am using to connect the N-class to the JBOD is 2 metres long.

NOTE: I should have mentioned this before - both the application and images repository that I am trying to copy across to the JBOD physically reside on a XP512 which has GB Fibre connection to the N-class.

I used the following command to do the copy:
find . -xdev -depth | cpio -pdvmu /mnt/destination_dir