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Daisy Chaining DLT7000's?

 
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James Anker
Valued Contributor

Daisy Chaining DLT7000's?

Hi,

Does anyoe know if you can "daisy chain" 2 x DLT7000's of 1 x A4800A FWD SCSI Card?

I know its not supported using DLT8000's but is this also the case with DLT7000's?

Points waiting..!

Thanks very much in advance.

James
6 REPLIES 6
Michael Tully
Honored Contributor
Solution

Re: Daisy Chaining DLT7000's?

Hi James,

No this is not supported either as far as I know. The problem you face is having more than one device of this type on a SCSI chain and the amount of data that gets streamed to the drive. Most of the time having one drive will have enough of a problem trying to keep up up with the data streaming enough (constant throughput) to not have the drive waiting for data.

There are plenty of postings such as this, where there is poor backup performance because of this scenario.

Cheers
Michael
"When I have rouble spelling, it's called fat finger syndrome."
Anyone for a Mutiny ?
Leif Halvarsson_2
Honored Contributor

Re: Daisy Chaining DLT7000's?

Hi,
It depends on how you want to use the drives. It should be no problem if they are used independent and not at the same time or if used sequential (for example a OmniBack device chain).
A. Clay Stephenson
Acclaimed Contributor

Re: Daisy Chaining DLT7000's?

Here's the rule:

A maximum of two ACTIVE DLT4K's per FWD bus; a maximum of one ACTIVE DLT7K or DLT8K per bus.

You can put any number (well, a maximum of 15) of drives on a single bus as long as you play by the above rules.

If you violate the rules, the drives will function almost perfectly - the worst kind of problem. Moreover, if a DLT is not supplied with enough data to stream its performance drops off most dramitically and also the stops/starts induce premature wear on the drive mechanisms.
If it ain't broke, I can fix that.
Bill Hassell
Honored Contributor

Re: Daisy Chaining DLT7000's?

As mentioned, the DLT drives are very fast and need a *LOT* of data very fast to keep the tape moving. When the tape drive is starved for data and the drive has to stop, backup and start over for the current record. If this happens for every 10 records, the throughput drops by two magnitudes (100:1 loss in performance). So a 1 hour backup could take 100 hours or about 4 days! And the excessive start/stop/repostition steps will quadruple the wear on the drive mechanism.

The DLT 7000 and 8000 require immense amounts of data that far exceed the bandwidth and driver speed for most SCSI bus cards if two or more are used at the same time. If you use one exclusively, then multiple drives can exist on the same bus. An example would be fbackup with multiple -f options. Each tape drive is used one at a time until it is full.


Bill Hassell, sysadmin
Angus Crome
Honored Contributor

Re: Daisy Chaining DLT7000's?

Using additional hardware, you can get this to work, however it is cost prohibitive. You are generally better off dedicating a drive per adapter.

If you want to try, you could buy two bus adapters to go from Ultra-2 SCSI (Single Ended) or higher to HVD and connect them that way. Could also be done with a SCSI multi-plex unit (if you can still find them).

I am absolutely sure these options would not be supported though, and cost a lot more than a second SCSI card, cable and terminator.
There are 10 types of people in the world, those who understand binary and those who don't - Author Unknown
Steven E. Protter
Exalted Contributor

Re: Daisy Chaining DLT7000's?

Even if it would work you are pushing the envelope for no good reason.

As Bill pointed out these drives need a lot of data. If they don't get it, the reason for buying them, performance will be lost.

You are a lot better off just getting another SCSI card.

We have our Ultrium drives on their own SCSI card all by themselves. Under those circumstances they perform wonderfully.

SEP
Steven E Protter
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