Disk Issues

We have a few "Early 2008" Mac Pro systems here at CFCL, including the one that sits near my desk. However, the graph processing explorations I have in mind really need more and faster resources (e.g., disk, memory, processing cores). Or at least, that's my rationalization for upgrading my primary machine (:-).

The 2013 Mac Pro is an elegant and powerful machine, but it isn't well optimized for my needs. For example, I don't need outstanding graphics performance, but I do need to add cards, disks, and so forth. So, I have purchased an older (mid-2010) Mac Pro and am using it as the basis for mauve, my new desktop machine.

In preparation, I have been upgrading the disk drives on my current machine. For example, I'm trading up from some 1.5 TB drives to 6 TB models. In the process, I have run into some annoying issues. Basically, various companies (e.g., Apple, Hitachi, Samsung) have made (and are making) backwards-incompatible, gratuitous changes:

See below for a detailed discussion...

Mac Pro Tray Design (Apple)

The disk trays are a very nice part of the old Mac Pro's design. Although they don't support hot plugging, they make it very convenient to add and remove drives, move drives between machines, etc. They also make it safe and easy to work with the disk mounting screws.

However, between 2008 and 2010, Apple made some gratuitous (and ill-considered, IMHO) changes to the tray's design:

  • The new trays are longer (even though the disks are the same size :-).
    It is not possible to slide a 2008 tray into a 2010 bay, or vice versa.

  • The captive mounting screws went to a smaller Phillips drive (#2 to #1),
    increasing the chance of stripping out the screw head (and forcing users
    to reach for a different screwdriver :-/).

What were they thinking?

Drive Design (Hitachi, Samsung)

In SFF Committee SFF-8301 Specification for 3.5" Form Factor Drive Dimensions, TABLE 3-1 describes three dimensions for "bottom mounting holes":

Dimension Millimeters Inches
A6 44.45 1.750
A7 41.28 1.625
A13 76.20 3.000

  • The back pair is located 1.625" (A7) from the connector area.
  • The middle pair is located 3.375" (A7 + A6) from the connectors.
  • The front pair is located 4.625" (A7 + A13) from the connectors.

Here is the requirement text from the specification:

The pair of bottom mounting holes located by dimension A7 is required. One additional pair of bottom mounting holes are required, either the pair of mounting holes located by dimension A6 or the pair of mounting holes located by dimension A13. Providing all three pairs of mounting holes (located by dimensions A7, A6 and A13) is allowed.

Apple's trays provide "captive screws" that fit the back and middle pairs of holes. The drive is suspended from four screws, ignoring the front pair of holes. Because most drive vendors support these pairs, this approach has worked well for the last decade. Recently, however, some drive vendors decided that (a) the front pair is superior and (b) the middle pair isn't necessary.

Unfortunately, this leaves the drive suspended from a single pair of screws (and the SATA electrical connections :-/). Obviously, this isn't a great mounting solution. I'm certain that I'll be able to rework the mid-2010 trays to support the drives, but this seems like a completely unnecessary hassle.

The drives in question (see below for a partial list) aren't cheap, so why are the drive vendors scrimping on mounting holes?

  • Hitachi OF13335 (6 TB SATA)
  • Seagate STBD66000100 (6 TB SATA)
  • Seagate ST8000AS0002 (8 TB SATA)

FWIW, I also ran into a problem when trying to mount a different drive (Western Digital WD60EZRX) on a 2008 Mac Pro tray. Specifically, the mounting holes were about 1/16" too shallow to allow the screws to be tightened. Sigh...

Archive HDD Performance

After I got the Archive HDD (Seagate ST8000AS0002) drive mounted, I found that:

  • Write access was unbelievably slow.

  • It couldn't handle files larger than 2 GB.

So, I returned the drive and bought a couple of "normal" 6 TB drives...


This wiki page is maintained by Rich Morin, an independent consultant specializing in software design, development, and documentation. Please feel free to email comments, inquiries, suggestions, etc!

Topic revision: r8 - 27 Apr 2015, RichMorin
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