SCSI performance reduction

[Bruno Misculin Rosamili]

I need to attach daisy-chained to the LVD SCSI port of a rp5450 server a DDS3 DAT and an ultrium 230 device.
I know that connecting togheter LVD and SE device I got a performance reduction.
The question is:
the performance of the LVD bus degrade from 80MB/s to 40MB/s or to 10MB/s

Thanks for every explanation.

Bye.

[Michael Tully · Accepted solution]

Hi,

Daisy chaining any type of DLT or LTO tape drives will seriously degrade performance. The problem lies in the fact that the LTO drive needs to keep streaming at a reasonable rate to ensure throughput. Sharing the chain between two drives will not allow the drive
to stream at a fast enough rate to write data to the tape at a rate you would expect. The best advice I can give is, invest in an additional SCSI card, it will be worthwhile.

Michael

[Marino Meloni_1]

hi

the dds3 is a "ultra 2" S.E. device, then: 40 MB/s 8 Bits
If you connect on the same bus than LVD devices, all the bus will be converted in SE mode
As previouly explained a Ultrium 230 need all the bantwith to Spream the data.
bye

marino

[Leif Halvarsson_2]

Hi
Will the two devices be used simultaneousy. I think this configyration can give "resonable" performance if only one device is used at the same time.

[Bruno Misculin Rosamili]

Considering that the DAT is normally unused and that the performance of Ultrium 230 is 15MB/s (30 compressed), do you think 40MB/s is enough to keep the tape always strained?

Thanks everybody

[Leif Halvarsson_2]

Hi
The Ultrium 230 has "adaptive tape speed" whitch mean that if you cant feed the device at full speed the drive will lower the speed to keep it streaming (not start and stop). This is a useful feature in many enviroments because you need a very high performance disksystem/network and other to stream the drive with 30MB/s.

[Marino Meloni_1]

hi
you should consider that the 40 MB/s is the total bandwith, the data over the scsi are usualy not constants, the whole band is used for the Burst mode, It will fill the buffer of the Ultrium, If you cannot keep full the buffe you will experience several issues.
I would suggest to buy a separated card for the DDS3 (SE device).

bye
marino