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How Drives works in MSL4048

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Rafael Botia Romero_1
Occasional Contributor

How Drives works in MSL4048

I have a HP StorageWorks MSL4048 Tape Library Fibre Channel, this library has 2 Drives and each drive in the rear has a dual FC connection, my doubt is if every fc works with the drive to that this one connected or if each FC can work with both drives.
9 REPLIES
Patrick Terlisten
Honored Contributor

Re: How Drives works in MSL4048

Hello,

you need to connect port A of each drive to you fabric. Multipathing is a special thing and not all backup applications support multipathing for tapes (for example Data Protector doesn't support it...). If you lose one connection, only the drive with the missing link would not work. Remember that the robotic is presented over the first drive. If this link fails the robotic can't be controled any more.

Best regards,
Patrick
Best regards,
Patrick
Rafael Botia Romero_1
Occasional Contributor

Re: How Drives works in MSL4048

Patrick

Thanks for your help, I understood about failover, but I'd like to know if the FC can have access to both drives or every FC can have access to one drive only.

Thanks
Patrick Terlisten
Honored Contributor

Re: How Drives works in MSL4048

Hello,

every drive has two ports. You can access each drive over both links, but it's not suppored. You should connect only one path to the fabric.

Best regards,
Patrick
Best regards,
Patrick
Rafael Botia Romero_1
Occasional Contributor

Re: How Drives works in MSL4048

Hello,

Is clear the issue about both FC ports, only port A must be connected. My question is exactly this. The FC port A can access the drive to another drive in another slot? (Remember my library has two drives) Thanks for your patience
Rafael Botia Romero_1
Occasional Contributor

Re: How Drives works in MSL4048

Hello,

I have another doubt... the medium changer or exchanger is present for both modules? I mean for both drives? or each drive has its own exchanger?

The situation is the libary is in another country and i did not work with this model of device.

Thanks a lot.
Patrick Terlisten
Honored Contributor
Solution

Re: How Drives works in MSL4048

Hello,

no, the changer is only presented by the first drive (AFAIK you can choose which drive will present the changer). If you connect only one drive, you can reach the other drive. The drives have no connection between.

Best regards,
Patrick
Best regards,
Patrick
S. Boetticher
Regular Advisor

Re: How Drives works in MSL4048

are you sure you didn't mistyped something? "If you connect only one drive, you can reach the other drive." vs. "The drives have no connection between" sounds contradictory...

IMHO to use both drives you need a FC cable to each one (Port A), at least that's how our MSL8096 works (should be similar). How would you send data to second drive if it won't be connected???

So, Tape1 FC-A is for tape drive and changer, Tape2 FC-A for that tape drive...

Besides feeding two LTO4 over one 4GB channel would be a performance bottleneck (a LTO4 can do up to 120MB/s plus compression, so a database-backup at 3:1 would be running nearly twice as fast if each drive would have it's own 4GB (400MByte/s) pipe...
Patrick Terlisten
Honored Contributor

Re: How Drives works in MSL4048

Hello,

sorry, it's a typo. It should be "you can't reach the other drive."

A LTO3 drives has a native write speed of 60 MB/s, a LTO4 80 MB/s. With a 2:1 compression ratio you need at least a 2 GB FC link for _one_ drive. So if you data travels over a single 4 GB ISL this could be a bottleneck.

Best regards,
Patrick
Best regards,
Patrick
S. Boetticher
Regular Advisor

Re: How Drives works in MSL4048

as I thought :-)

your speeds are for the half-height drives, we use full-height that have 80 (LTO3) and 120 (LTO4) MB/s + compr.

I'm really happy with the direct link for each drive (our databases are 4-5:1 compressible), so on our old MSL5052S2 with SDLT320 and the NSR1200-160 we were not able to stream more than one drive (there is a 80MB/s Limit per BUS for the hotswap drives on the old library, so one stream nearly saturaded already the bus...)