cecs - Fotolia
We created a TAN (Tape Area Network). The TAN consists of a Brocade 3800 (2Gb) FC switch, FC_AL only LTO tape units and several hosts (utilizing a third HBA). I have read that the Brocade supports Fibre Channel translative mode meaning that it will do the translation from FC_AL to FC_SW and vice versa. The HOSTs are able to backup data on the LTO Tape Units, but the speed is not what we expected.
The only question I have is, what is the overhead that is involved in the translation process from FC_AL to FC_SW? Will it be faster if I had all the hosts using FC_AL? FC_SW is a faster method since we are using a switch, but does the translation slow it down.
There is some overhead within the switch when bridging between protocols, but I have no statistics on what that is. The feature you are referring to is called QuickLoop on Brocade. A QuickLoop enables connectivity into a switched fabric of legacy FC-AL devices. Address translation is performed within the switch so that all devices within the QuickLoop are accessible to fabric-based nodes.
Each QuickLoop on a switch can provide the full bandwidth of the switch port for devices connecting into the loop. Loop devices share the bandwidth of the port. Each port can be configured as a looplet, running at the port speed. This means you can load balance access to your tape drives by spreading the load on different looplets.
Try setting up multiple switch ports within the QuickLoop and spread the tape load across those ports. This should dramatically increase performance. Other things to consider when doing SAN based backup is the "feed speed" of the disks to the tape. The whole idea is to provide enough of a data stream to keep the tape moving across the tape heads without the "shoe shine" effect. When a data stream is interrupted, the tape needs to reposition itself on the heads to continue. This causes a "stop start" or "shoeshine" motion on the tape device that slows down performance. The feed speed is the maximum throughput of reading data off the disks, and sent to the tapes. Using "serverless" backup can help here because data moves directly from disk to tape via the "e-copy" extended copy command.
Check with your tape vendor for best practices in performance tuning with their solution.
For more information on QuickLoop capabilities, check out Brocade's Web site.
Your practice of using a separate TAN with a separate adapter in the host is a good one. This will provide non-impact backup during the day.
Editor's note: Do you agree with this expert's response? If you have more to share, post it in one of our .bphAaR2qhqA^0@/searchstorage>discussion forums.
Dig Deeper on Tape backup and tape libraries
So what is SAN School? If this is the first time you are asking yourself, "What's a SAN?" -- SAN School is for you. If you are implementing your first SAN and need implementation and migration help -- SAN School is for you. If you are far along in the SAN process and need to extend your SANs or connect SAN islands -- SAN School is for you.
The authors of "Storage Area Networks for dummies", Christopher Poelker and Alex Nikitin, are your SAN School professors. Through 15-minute Webcast lessons, they covered SANs from A to Z, from what a SAN is, to connecting those last nodes for optimal performance.SearchStorage.com readers sent Chris and Alex received a lot of questions during each SAN School Webcast lesson. Since each lesson only lasted 15 minutes, they weren't able to answer all of your questions. Thanksfully, though, Chris Poelker was kind enough to answer them after each lesson.
The editors of SearchStorage.com have taken each of your questions and Chris's answers and posted all of them for you here. Also, if you missed any of teh SAN School Webcasts, click here
Related Q&A from Christopher Poelker
SAN expert Chris Poelker discusses how to change the size of a LUN in a Microsoft cluster server environment. Continue Reading
SAN expert Chris Poelker compares connecting a SAN with wavelength cabling and dark fiber and discusses the pros and cons of each. Continue Reading
Storage expert Chris Poelker outlines WWN basics in order to answer the question: "Why do HBAs in a SAN have same base?" Continue Reading
Have a question for an expert?
Please add a title for your question
Get answers from a TechTarget expert on whatever's puzzling you.