SAS vs SATA

I involuntarily received a crash course in storage acronyms and technology (in that order) recently. Here are a few notes.

VMware ESX Server really likes to have its VMFS (the file system for virtual machine disk images) on SCSI disks, if they’re on DAS (directly attached storage). Another option is to use a SAN (storage area network) or a simple NFS (network file system) server. I don’t have expensive network storage devices, so I need to install SCSI equipment in my machine.

These days SAS (serial attached SCSI) and SATA (serial ATA) are the interfaces of choice. It turns out that there is significant interoperability between them. All of the SAS controllers I’ve found also support SATA drives. The reverse is not true: one cannot attach a SAS drive to a SATA controller.

Today I ordered an Adaptec SAS-3405 SAS controller and a Fujitsu MAX3147 SAS 147GB hard drive. From everything I’ve found to read these two should play well together, giving me further options to attach more SAS and SATA drives as I see fit.

The one question that remains in my mind is whether the cable included with the controller will work correctly for the SAS drive, or if it only accepts SATA drives (suggesting that I need to buy another cable, which would be troubling because I did not order one). Wikipedia shows some SAS connectors, but no pictures of drives to calm my nerves. Here are Wikipedia’s pictures of SATA connectors.

This PDF from HP suggests that a cable that fits onto a SAS drive will also fit onto a SATA drive. It also suggests that a traditional SATA data cable will not attach to a SAS drive.

The Adaptec controller that I ordered includes a 2247100-R cable, which can be found on theAdaptec SAS cables page. It looks like it fans out to traditional SATA connectors, and therefore will not allow the connection of a SAS drive. Its exact description is “mSASx4 (SFF-8087) to SATA (4)x1 with sideband (SFF-8448)”. So, I’ve learned that the connector on my controller card is an SFF-8087. The SFF-8087 appears on Wikipedia’s SAS page, as does what looks like the correct connector for a SAS drive, the SFF 8484. Note that the “sideband” connector that comes with my controller is of no use, since 8448 != 8484.

It looks like the cable I really want is the 2231900-R from that Adaptec SAS cables page. It also appears that an SFF-8482 is an SFF-8484 but with the ability to remove the power cable portion of the connector (useful for compatibility with PATA (parallel ATA) drive power connectors).

Hopefully ESX Server will be happy with the Adaptec controller and a SATA drive, and I can just return the SAS drive. Otherwise, I’ll need to order one of those 2231900-R cables.

Good times.

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