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Which External SDLT 320 to buy

Robert Popoff
Occasional Visitor

Which External SDLT 320 to buy

I have a Proliant 1600 and need to know whether to purchase a High Voltage SDLT320 or Low Voltage SDLT320.
11 REPLIES
Joshua Scott
Honored Contributor

Re: Which External SDLT 320 to buy

Depends. What SCSI cards do you have installed in this server?

look at the bottom of these pages:

http://www.pcguide.com/ref/hdd/if/scsi/protDiff-c.html
http://www.pcguide.com/ref/hdd/if/scsi/protLVD-c.html

And then check the external connector on the proliant to see if you have a LVD or HVD SCSI connector.

HTH!

Josh
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Robert Popoff
Occasional Visitor

Re: Which External SDLT 320 to buy

Ok, The documents were helpful but still a bit confusing. I found the icon on the server and it is the Single Ended (SE) icon. Does this mean Single Ended High Voltage? The document is labeled Single Ended (SE) and Differential(High Voltage, HVD) Signaling
Joshua Scott
Honored Contributor

Re: Which External SDLT 320 to buy

You should get the Low Voltage SDLT320.

Low Voltage is compatible with SE SCSI.

Josh
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Leif Halvarsson_2
Honored Contributor

Re: Which External SDLT 320 to buy

Hi,

I am confused, is there a SDLT with HVD interface avialable ? I can only find LVD interface.

The LVD interface is compatible with SE.
Robert Popoff
Occasional Visitor

Re: Which External SDLT 320 to buy

Thank you very much!
David Ruska
Honored Contributor

Re: Which External SDLT 320 to buy

You want to stick with LVDS, since it supports higher transfer rates than HVDS, and gives you almost as much cable length.

The SDLT320 can run 80MB/Sec burst. HVDS SCSI is limited to 40MB/Sec.

You don't want a SE controller to an LVDS drive, since it's limited to 40MB/Sec and less cable length.

Also, I think all the SDLT drives are native LVDS, and would require a converter board to make an HVDS drive (another thing to fail).

The journey IS the reward.
Joshua Scott
Honored Contributor

Re: Which External SDLT 320 to buy

The SDLT320 only has a native transfer rate of 16MB/s. The UWSE connector on the Proliant is 40MB/s. Most likely this won't cause problems, but if you want to make sure, get a SCSI card, like a Adaptec 29160 card.

Josh
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David Ruska
Honored Contributor

Re: Which External SDLT 320 to buy

> The SDLT320 only has a native transfer rate of 16MB/s.

That's the native (uncompressed) rate - it can run at least 32MB/sec with compressed data (not sure at what point the compression engine limits). The interface burst rate is 80MB/sec, which is the rate you can write to the drive's buffer. Even though the drive can sustain about 32MB/sec to the tape, the faster burst rate helps in keeping the drive streaming when the host rate varies.
The journey IS the reward.
Joshua Scott
Honored Contributor

Re: Which External SDLT 320 to buy

David,

not to nitpick, but the compressed rate is only a measure of how much native data on the system is being backed up. The actual amount of bytes transfered to the tape never exceeds 16MB/s

for instance if you had a 32MB file on the server, it would theoretically be transferred over in 1 second. But it would be compressed into a 16MB chunk first.

Josh
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David Ruska
Honored Contributor

Re: Which External SDLT 320 to buy

I love to nitpick :-)

The compression happens inside the drive. The fixed rate is going to tape. If the data compresses 2 to 1, then you will actually get 32MB/sec on the host-to-drive bus.

(BTW, I developed the first tape drive with built-in data compression - the HP7980XC).
The journey IS the reward.
Joshua Scott
Honored Contributor

Re: Which External SDLT 320 to buy

I stand corrected.

However, (back to the original question) the 40MB/s should be sufficient for the tape drive (assuming compression is not more than 2.5X)

Josh
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