HPE MSL G2 LTO-8 ... F.C. multipath question

[WillyEB70]

Dear all

a few days ago, I received an HPE MSL G2 Autoloader library No. R1R75A with an LTO-8 FC drive. I already had an Almalinux 9.4 HPE Proliant DL560G8 server with two 8Gbps HBAs and a SAN network with two HP 8/20Q.

I configured the zone in the SAN, installed the library, and set up the server. The Linux server correctly sees both the drive and the autoloader. With the MTX command, I can load the tape into the drive, and with the command tar -cvf /dev/st0 file, I can write to the tape.

Keep in mind the LTO drive has two fiber Gbics that I connected to two switches for HA.

So the problem is that the server sees two drives and two autoloaders: /dev/st0, /dev/sch0, /dev/st1, and /dev/sch1.

I used the multipathd program to manage the two paths, but I have not been able to resolve the issue.

My question is this: Can the multipathd service manage 'character' devices, or can it only handle block devices like storage?

If multipathd can manage character devices and thus the MSL libraries, can you provide a configuration file for /etc/multipath.conf?

Thanks a lot

Best Regards

Willy

[Cali]

Hi,

typical the Tape is only connected with one Path (Cable).
The default MPIO Driver of most OS only supports Multi Path for Disk and not for Tape.

HPE has a dedicated Multi Path Tape Driver for some OS, but it is not free, you need to buy a Multi-Path Tape License and check, if your OS is Supported.

For Linux, the driver will be compiled on the machine on which it will be installed.

More Information about is here: HPE StoreEver Tape Libraries LTO-7+ Path Failover User Guide

Cali

[Curtis_Ballard]

Cali shared a good reply above - for OS level multipath with tape devices you need the dedicated multipath driver.  Linux multipathd does not have support for tape or media changer devices.

With tape there are some applications that also support multipath at the application layer.  Those applications are able to use multiple paths to the tape devices and inside their software they are able to detect when multiple devices at the OS level are actually multiple paths to the same tape device and then the software will select one path to use and use any other paths to the same device for failover.  To do that the software has to track the operations and have recovery code that determines the state of the tape drive, or the media changer, following a path failure after which the software can send the appropriate recovery commands.  For writes to the tape drive that usually means creating checkpoint locations where the tape location and the association with the data being written is recorded then following a path failure performing a rewind to that known position and resuming from there.

If you have an application that explicitly states that it supports tape multipath then you can use both ports and multiple paths without the path failover driver.  Support for that has to come from the software provider.

[WillyEB70]

Dear all,

If I can't manage failover with multiathd I'll try to understand if with Bacula Community edition I have this possibility.
One last thing, I connected the library's ethernet card with my private network and I manage the MSL via web,  but what is the ethernet card in the LTO-8 for and what is its default IP address?

Thanks for your answers.

Best Regards

Willy

[Cali · Accepted solution]

See here: Data Verification
https://support.hpe.com/hpesc/public/docDisplay?docId=a00037685en_us&page=GUID-D7147C7F-2016-0901-0367-000000000509.html

Note: To use it you need a "Data Verification Software License" and "Command View for Tape Libraries", both of which are not free.

Path failover also requires an extra license.
https://support.hpe.com/hpesc/public/docDisplay?docId=a00037685en_us&page=GUID-EC038CC6-8A83-4B5D-A184-5779DEA8E5F9.html#ariaid-title1

Cali