My project is expanding 24-HDD ZFS box by adding 45-drive box with option to add another 45-drive box later (all are JBODs).
Host box (24 HDDs) is Supermicro with single port expander backplane and LSI RAID card (I think, MegaRAID SAS 9240-8i). Currently backplane occupies one SAS port on card, leaving 1 port open.
My current understanding is that on first level, RAID card has to support number of drives I want to have via expanders. So I need to change RAID card to something supporting 128-drives.
After that I should be able to expand by daisy-chaining: Host backplane expander -> host RAID card <- extension 1, backplane 1 (24 HDDs) <- extension 1, backplane 2 (21 HDDs) <- extension 2, backplane 1 (24 HDDs) <- extension 2, backplane 2 (21 HDDs)
My RAID setup is volumes of 4 or 5 vdevs, RAIDZ2 (RAID6), 4TB SAS drives
Questions: Will daisy-chaining of 2 or 4 backplanes preserve 6Gb/s speed? Is the only limitation is number of supported disks by RAID card?
Also, as I understand, use of dual-expander backplanes allows redundancy by connecting backplanes by daisy-chaining via additional paths. Is that true and is it worth extra 200$?
Should I throw away RAID card and use HBA instead since it will allow support for 128 drives cheaper and all I care is JBOD?
I used these sources to get understanding:
- SAS Expanders
- Supermicro SC847J SAS2 chassis manual
- Do SAS expanders work transparently with SAS controllers?