October 14, 20169 yr I've been running some of my drives in an external chassis, connected via an LSI 9200-8e HBA. I just picked up an HP SAS Expander, partly so I'd be able to put more than 8 drives in that chassis, and partly so that the external SAS cables would be using SAS signaling rather than SATA. I have both ports on the LSI connected to the expander, in hopes of dual-linking it for greater bandwidth. So far everything's working, but I don't see any sign that the thing is dual-linked. The expander only shows up once in lsscsi, and nothing in the logs seems to indicate a link speed or number of lanes. Right now the number of drives that are connected wouldn't necessarily exceed the bandwidth of a single lane, so I can't just hammer on everything and benchmark to see whether it's working. Is there anything I can check to verify that it's doing what it should be doing?
October 14, 20169 yr Dual link should work without issues with the LSI, only way I know to check is to test the bandwidth, since the HP expander using SATA disks only links at SATA2 speeds, it's not difficult to exceed a single link, which is ~1100MB/s, so depending on how fast your disks are you don't need that many to reach that during a parity check.
October 14, 20169 yr Author Well, the combined raw speed of the drives that are attached to it at the moment is around 1250MB/s, and it doesn't seem to have a problem reaching that, so that's a good sign. Although, I thought the v1.52 firmware that added support for SATA-2 drive speeds (on the green HP expanders) also added support for 6G SAS links. In that case, wouldn't the single-link performance between that and the LSI card be closer to 2400MB/s?
October 14, 20169 yr Author Actually, I guess the simplest thing at this point would be to toss a couple more drives on the expander, and try the test with and without the second SAS cable connecting it.
October 14, 20169 yr With SAS disks you'll get 2400MB/s per link, with SATA2 disks 1200MB/s per link, ~2200MB/s and ~1100MB/s respectively "real world" max speed. Testing a single link should confirm, max speed will be 1100MB/s divided by the number of disks.
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