Surestore DLT vs 80e

[Rupert Heesom]

Tape drive on HP Netserver E60 using the built in scsi controller (I think Adaptec 3940 UW dual channel).

On the same scsi channel is a RAID disk drive (individual RAID disks listed under scsi bios when booting). Both the tape drive and RAID drive are daisy chained externally (on the same external channel).

I have 103Gb to backup, and the transfer rate I'm getting is way too slow.

The manual for the tape driver specifies that using burst mode I should get a transfer rate of 20MB/sec on an LVD bus.

I'm getting more like 1 to 2MB/sec.

Questions -

1) I would like to know when to expect the scsi controller to use burst mode.

2) Lots of the files to backup are audio files (WAV & MPEG). I assume that because these are binary & compressed anyway, that trying to use any compression during backup isn't going to work.

3) How to use SCSI channels for max throughput? I gather from the tape manual that the tape drive is an LVD device using an Ultra Wide SCSI-2 interface.
( any difference between "Ultra/Wide" and "Wide/Ultra"? )

The docs I've seen for the SCSI controller on the server
indicates that it only supports single-ended, not LVD devices. Thus I assume that the tape drive is being forced into single-ended mode.

I don't know the RAID drive specs, but I assume that this RAID drive will also be forced into single-ended mode.

I'm thinking of putting the tape drive on it's own controller. However, if I do so and it's able to support a transfer rate of 20MB/sec, will the RAID and other drives be able to feed data at 20MB/sec in single-ended mode?

OS used: Windows 2000 Advanced Server, SP2.

regs
Rupert Heesom

[BR19682]

Hi there.
Daisychaining is more likely the problem.
DLT drives should never be dasiychained with something else.
Reason :
Device does not go into streaming mode ( continously writing to tape ). The amount of data coming from the scsi interface is not fast enough. A DLT80 will use all bandwidth of the controler. Otherwise it writes data to tape, rewinds the tape, repositions the tape to last writing mark, write data etc. .
Rgds
Alexander M. Ermes

[Rupert Heesom]

Thanks for your reply!

I wondered whether you could answer any of my other questions? Ie: the "Ultra/Wide" vs "Wide/Ultra"? (Is there any difference in the two expressions?)

I also wondered which SCSI controller has the correct external connector? HP have told me to go for the 29160LP, however (according to an Adaptec PDF) this controller has a VHD 68pin connector, and the tape drive manual says the tape drive takes a HD connector.

Assuming I can pursuade my management to buy another controller, I don't want to buy the wrong thing! :-(

I want to give you lots of points for your trouble in answering me, but I thought I'd make you work for it! :-)

regs
rupert heesom

[Rothery Harris · Accepted solution]

Dear Rupert,

The DLTVS80 tape drive is an Ultra-2 SCSI device and has a 68pin HDTS connector. You will never achieve decent performance running your drive on the RAID card. You should purchase a separate SCSI controller. This should be at lease a Ultra-2 SCSI device (AHA2940UW). The HP recommended product is the C7474A. You will need a 68pin HDTS to 68pin VHDCI SCSI cable. (VHDCI-Very high density.) - This is included in the C7474A kit.
I am sure your RAID card will supply the data fast enough for a DLTVS80.
The 'burst' rate for Ultra-2 SCSI is 80MB/s and is the rate at which DATA transfers take place on the SCSI bus. This does not include SCSI commands etc. The sustained data rate is governed by the rate at which the tape drive can write data (providing data is available in the tape drive buffer). This is 3MB/s without data compression. If your data can be compressed then better effective data rates can be achieved.

Rothery

[Rupert Heesom]

Thanks for your msg, Rothery.
Thats exactly the sort of info I'm looking for!

One more Q though.... you mention the tape data rate is 3MB/sec uncompressed. The tape manual talks about a burst data rate of 20MB/sec. Now you've defined the burst rate as the controller data rate (assuming no device is slowing the controller down).

You seem to be saying that although the tape drive might be able to accept data at 20MB/sec from the controller, it can only write at a speed of 3MB/sec. I was hoping for a backup speed of 20MB/sec! I guess I will be disappointed!

(I will not be using compression since many of our files are audio MPEG or WAV files, ie already compressed).

regs
Rupert

[Rothery Harris]

Dear Rupert,

The burst rate remains constant as it is defined as the rate for a data transfer between initiator and target. When other devices is present they wait for the bus to become free. Other devices cause an overall slow down not because they slow the burst rate but because you may have to wait to take ownership of the bus. This is performed by the bus arbitration if several devices are contending.
Your device will not backup at speeds greater than 3MB/s as this is a constant rate. Although you may be transporting chunks of data at 80MB/s it cannot drain the buffer at greater than 3MB/s.

regards

Rothery

[Rupert Heesom]

Thanks for that answer.

It's good to learn more about how devices work!

regs
rupert