DF & SE Same Bus?

[Justin Willoughby]

I am guessing no but I thought I would ask any ways.

I have a Jamaica enclosure with two DDS3 tape drives in it. I am guessing I can't put two 9.1GB DF drives in this same enclosure on the same bus as the tape drives right? The tape drives are SE.

Also I have room in a different Jamaica enclosure where my root disks are. If I install two 9.1GB drives in this enclosure for use with my database (on the same scsi bus) and use Mirror/UX to mirror the LVs on these new disk will have performance problems?

Currently our root disks consists of one 4GB and one 9GB that are mirrored (4 disks total).

I want to add two more 9GB disk to extend a database onto. I just want to make sure the scsi bus will not become over loaded by doing this.

Thanks!

- Justin

[Leif Halvarsson_2]

Hi
I will not recommend mixing tape drives and disks on the same bus, and not mix different SCSI interfaces (for example wide and narrow SE or LVD). In some cases it is possible but there is a big risk the performance will decrease. Adding more disks (of the same type) to one SCSI bus is possible but in your case, to get best performance I think you should add a new SCSI-HBA.

[Justin Willoughby]

Thanks Leif,

Adding these disks is only a short-term solution. We are running low on space and do have our SAN running yet.

Is it possible to max out the scsi bus buy having to many disks attached and/or accessing two disks from an application and the others from the OS (HP-UX 11.0 OS Boot Disks)?

Thanks!

- Justin

[Leif Halvarsson_2]

Hi
You can add as many disks as it is possible depending on the type of bus (7 for narrow, 15 for wide). And you can use the different disks as you like (some disks for OS, other for a database and perhaps other for user files). If several of the disks is heavy loaded there can be a risk for performance problems, but in most cases is the different disks not active at the same time (for example is there is normally low activity on a OS disk). And as this is a temporary solution I think this is acceptable.

[Michael Lampi]

Assuming your DF (differential) SCSI drives are HVD and not LVD, then you can NOT place these on the same SCSI bus as the DDS3 tape drives without the use of a HVD to SE SCSI bus converter.

Also, assuming that your DDS3 drives are on a narrow (50 pin) SCSI bus, then there is no way that you will be seeing high performance disk I/O on that bus. The maximum throughput that this narrow SE SCSI bus has is 5 megabytes/second.

If the DDS3 drives are on a wide SE Ultra SCSI bus, then by adding disk drives to this bus you are at risk by having too many devices on the bus, as well as having cable lengths beyond the maximum supported by the Ultra SE SCSI standard. This will be indicated by an increase in SCSI bus errors, possible data corruption, etc.

What type/model of system is this that you are using?

[Eugeny Brychkov · Accepted solution]

Hello Justin,
Jamaica JBOD (HASS) has 2 separate disk busses (but they can be daisy chained). Any bus can contain only DF devices (disks with purple "DF" label) or SE devices (disks/tapes with yellow "SE" label). You can't mix SE and DF devices on one bus. Of course, bus with SE devices should be connected to SE SCSI controller, and bus with DF devices - to DF controller.
Please look at basic rules of disk subsystem perfomance under HPUX:
- use separate disks for root and swap lgical volumes;
- use mirrored disks connected to different SCSI buses (controllers) (also HighAvailability rule);
- do not use more than 4 disks on one bus if you have high SCSI bus activity. Disks with SCSI address of lower priority (7->0, 15->8) can be observed generating "PV failed" in syslog with following "PV restored" event. If this will occur try to increase timeout for disk using "pvchange".
Hope it will help.
Eugeny

[Xavier Gutierrez_1]

Hi, Justin.

The answer is NO, YOU CAN'T.

The DF disks for Jamaica enclosures are High Voltage Differential and the DDS3 drives are Single Ended (that is, LOW VOLTAGE).

So, they're electrically incompatible.

Best regards.

[Justin Willoughby]

Thanks for all who replied!

I appreciate it! I thought the answer was no and know I know for sure that is correct.

Thanks again,

- Justin