Mac Pro as RAID System (5, 1E, 1+0, ?) RocketRaid?

[cutterman]

Instead, use an internal to external MiniSAS cable. This will work with SATA disks (been there done all of this, so it's definitely not opinion; never thought the contact resistance would have been siginificant enough to cause all the problems that occured, but I was absolutely wrong on that one ).

What would be the down side of using an external enclosure with SAS expander (aside from cost)? I am looking at this option to connect an 1880ix card to an external RAID 5 array of SATA disks, since the card only has 1 external connector. There is a 15 drive 6G enclosure/sas expander on pc-pitstop that would provide space for future growth. I wonder though if the single connection restricts bandwidth at some point when expanders are used. Also would the internal to external adapters work reliably with a SAS expander connection? Thanks.

 

[nanofrog]

What would be the down side of using an external enclosure with SAS expander (aside from cost)? I am looking at this option to connect an 1880ix card to an external RAID 5 array of SATA disks, since the card only has 1 external connector. There is a 15 drive 6G enclosure/sas expander on pc-pitstop that would provide space for future growth. I wonder though if the single connection restricts bandwidth at some point when expanders are used. Also would the internal to external adapters work reliably with a SAS expander connection? Thanks.

The external port = 4 SATA/SAS ports, which have a bandwidth limit (540MB/s * 4 = 2160MB/s max sustained throughput). There's also some overhead associated with SAS expanders (similar to Port Multipliers, as they essentially do the same thing). Another thing to note, is it's an 8x Gen 2.0 card (500MB/s * 8 = 4GB/s sustained throughput for the entire card; PCIe slot is the limiting factor here).

In this particular card series, the additional ports are a nice way to get additional drives attached without the need for more expensive enclosures (SAS expanders) to increase throughputs via drive parallelism.

It's up to you, but I'd keep it one port per disk, as the SAS expander is likely only going to add costs ideally, but in reality will have a performance penalty as well (not horrible, but it's switching between disks = added latency), but the internal to external cables previously linked are a better solution (no performance penalty), and they're usually cheaper too.