There is a some bonus's to having it across the shelves though from what I have read in the Clariion Best Practices For Fibre Channel guide there is very little performance gains. If you build raid 1_0 across DAE's properly, you can loose one of those shelves and still have data availability.
Lookup in the guide: Binding RAID groups across buses and DAE's.
When working with the older FC4500/4700 Clariions it was a good practice not to have Raid-5 Groups created across different shelves to prevent a Raid-5 group from loosing more than two drives at one time.
With that being said in the 10 years working with the Clariion line I've never had just a single shelf in an Array fail, but I still try to keep Raid-5 groups on the same shelf when possible....
While the OP is on a CX3, and the EMC CLARiiON Best Practices for Fibre Channel Performance and Availability, FLARE revision 26 applies, he might also want to read the EMC CLARiiON Best Practices for Performance and Availability, FLARE revision 28.5.
This document includes additional information on vertical (multi-bus) vs. horizontal (single-bus) provisioning. In particular, it includes a larger discussion of failure implications of vertical provisioning in the RAID group provisioning section.
In addition, the EMC CLARiiON Storage System Fundamentals for Performance and Availability available on Powerlink later this month contains a higher-level discussion in the Performance Effect of Buses section.
Several documents have already been pointed out which contain excellent information on this topic.
From a real world customer experience perspective I can tell you that I've been working with CLARiiON arrays since the FC4700-2 with FLARE 11. I've used every major FLARE revision and every model of array up to the current models and FLARE.
We have a Best Practice to avoid RAID5 groups spanning DAEs. Sometimes we have done it anyway when it made sense. We don't have any concern with RAID 1 or 1/0 spanning DAEs as long as they are built with the mirrored copies on the seperate DAEs.
We have never had a performance problem associated with this configuration and we have never experienced an outage due to spanning DAEs.
That isn't to say that it can't (or won't) happen, but it does tell me that this isn't something that needs to be worried about too much. As long as you are aware of what you are doing and why you are doing it, you probably won't notice the difference except under a very specific (and rare) set of circumstances. So read all the documentation and the only one who can make the right decision on THIS question is you
mpalumbo1
50 Posts
0
April 17th, 2009 09:00
Lookup in the guide: Binding RAID groups across buses and DAE's.
rr_phx
26 Posts
0
April 17th, 2009 09:00
With that being said in the 10 years working with the Clariion line I've never had just a single shelf in an Array fail, but I still try to keep Raid-5 groups on the same shelf when possible....
jps00
2 Intern
•
392 Posts
0
April 17th, 2009 10:00
This document includes additional information on vertical (multi-bus) vs. horizontal (single-bus) provisioning. In particular, it includes a larger discussion of failure implications of vertical provisioning in the RAID group provisioning section.
In addition, the EMC CLARiiON Storage System Fundamentals for Performance and Availability available on Powerlink later this month contains a higher-level discussion in the Performance Effect of Buses section.
Allen Ward
4 Operator
•
2.1K Posts
0
April 17th, 2009 12:00
From a real world customer experience perspective I can tell you that I've been working with CLARiiON arrays since the FC4700-2 with FLARE 11. I've used every major FLARE revision and every model of array up to the current models and FLARE.
We have a Best Practice to avoid RAID5 groups spanning DAEs. Sometimes we have done it anyway when it made sense. We don't have any concern with RAID 1 or 1/0 spanning DAEs as long as they are built with the mirrored copies on the seperate DAEs.
We have never had a performance problem associated with this configuration and we have never experienced an outage due to spanning DAEs.
That isn't to say that it can't (or won't) happen, but it does tell me that this isn't something that needs to be worried about too much. As long as you are aware of what you are doing and why you are doing it, you probably won't notice the difference except under a very specific (and rare) set of circumstances. So read all the documentation and the only one who can make the right decision on THIS question is you