Date: Tue, 04 Feb 2014 22:27:16 -0600 From: Graham Allan <allan@physics.umn.edu> To: freebsd-fs@freebsd.org Subject: practical maximum number of drives Message-ID: <52F1BDA4.6090504@physics.umn.edu>
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This may well be a question with no real answer but since we're speccing out a new ZFS-based storage system, I've been asked what the maximum number of drives it can support would be (for a hypothetical expansion option). While there are some obvious limits such as SAS addressing, I assume there must be more fundamental ones in the kernel or drivers, and the practical limits will be very different from the hypothetical ones. So far the largest system we've built is using three 45-drive chassis on one SAS2008 (mps) controller, so 135 drives total. Over many months of running we had several drives fail and be replaced, and eventually the OS (9.1) failed to assign new da devices. It was time to patch the system and reboot anyway, which solved it, but we did wonder if we were running into some kind of limit around 150 drives - though I don't see why. Interestingly we initially built this system with each drive chassis on its own SAS2008 HBA, but it ultimately behaved better daisy-chained with only one. I think I saw a hint somewhere this could be to do with interrupt sharing... Thanks for any insights, Graham
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