The problem starts with having more tape drives behind each Fibre Channel port than the port can actually support.  This often happens when you're sharing a bunch of tape drives between several servers.  For example, say you're sharing 20 tape drives between 10 servers, and 10 are available via one FC port, and 10 are available via another FC port. 

If each server gets two tape drives, everything's fine.  Even if a given server grabs two tape drives on one FC port, that port can usually handle streaming two tape drives. 

BUT, what if a server want's four tape drives, and is able to grab them?  NOW what happens if it grabs all four tape drives from the same port?  Now the four tape drives are sharing a single FC port that can only handle two tape drives.  

But if the backup software were SMART, it would attempt (if it could) to grab two tape drives from each of the two FC ports.  But I don't see any backup software products doing this.

Do you? 

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schweeb   | 68.43.253.xxx | 2008-04-25 18:04:52 On the software side, I know the IBM Atape driver can handle multipathing... not sure if it can round robin or how it handles things. It's a start at least... Might want to look into actual appliances to do this type of thing. I think you could set something like this up via StorageTek SN6000 (which I think is EOL, and highly unreliable IME). You would present a set of virtual drives to the system via ACSLS... say, 2 per FC port... and the SN6000 would send the data to any physical drive that was available behind it. There may be something from Falconstor that would be appropriate as well. Neither of these exactly fit the bill for what you want, but with some ingenuity you can combine technologies to achieve this goal, I believe.

cpreston - My favorite combination (not)   | Super Administrator | 2008-04-25 18:07:00 ACSLS & the SN6000... Two products I love SO much... NOT.

schweeb   | 68.43.253.xxx | 2008-04-25 18:59:40 haha, agreed. I had a party when I got rid of my SN6000 3 years ago, in favor of EMC CDL. The best part was whenever I would put in a support call, and none of the Sun/STK guys had much of a clue as to how the thing worked, it was just voodoo magic. The solution to every problem was rebooting the SN6000 and ACSLS in the right order.

ddierickx   | 170.86.15.xxx | 2008-04-29 09:02:08 i don't know of anything like that, but on NBU you can limit the max amount of drives to use, so that way you could impose a limit of the amount of drives to use at once.

BStephens   | 144.160.98.xxx | 2008-05-01 12:14:26 I can't count the number of times we have asked Symantec to make Netbackup HBA aware and load balance across them. To date there is nothing you can do but limit the number of drives the server has access to so as to not overload an HBA. The problem with the limit max number of drives is you end up having to set the number to the maximum number you would allow on any one HBA.

pclifford     | 207.250.166.xxx | 2008-05-05 12:38:15 Maybe I am strange, but I hate backup. Traditional Backup. As we all know, it is about restoration, not backup, and recovering anything from tape is brutal. We spend a majority of our time helping to design solutions that eliminate "backup" by building on the ability to restore files, systems, and sites. Obviously, files must be restored instantly, and systems in a boot cycle, and then sites in a time frame that makes fiscal sense. All this can be done, thereby relegating tape to archive, not primary restoration. The larger the amount of data, the more this approach makes sense. If I am not mistaken, the amount of data continues to grow at incredible rates making this type of approach even more imperative. Paul Clifford Davenport Group www.davenportgroup.com

cpreston - Nothing is right for everyone   | Super Administrator | 2008-05-05 13:13:05 First, I agree that it's not about backup; it's about restore. I disagree that backup = tape, or even that backup = what you would think of as backup software. I'd also say it's about balancing restore speed (RTO) to system cost. Not everyone has the requirements to drive them to the types of systems you're talking about. Traditional backup meets the requirement of 90+% of applications. Near-CDP & CDP are great, but why use the more expensive, more complex solutions if the customer has no requirement to do so? Finally, a traditional backup system can also be a framework for controlling all the different ways you are protecting your data. I hope you enjoyed the free plug for your company. Maybe I'll go over to your user group and post a free plug for my site.

Aronar   | 62.255.240.xxx | 2008-05-12 10:54:16 Hi, Surely this is a capacity planning thing... If you have 10 tape drives that could all be used at the same time then you'd need to distribute them across multiple fibre channel ports to ensure you have enough bandwidth. For LTO3 drives for example at 78MB/sec native you've need 5 2gbit FC ports for 10 drives so 10 ports for all 20 drives. I've come across a similar situation recently and had to advise the customer to install more HBAs as they simply couldn't handle the bandwidth.

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