Slashdot Mirror
Going Deep Inside Xserve Apple Drive Modules
adamengst writes "If you've had an Xserve drive fail, you may have considered saving some money by putting a replacement drive inside its Apple Drive Module. That may be a false economy, though. TidBITS explains why, while pinning Apple down on exactly what goes into Apple Drive Modules and why they cost so much more than bare retail drives."
While I hate to copy it, the server being pummeled and reporting errors for 9/10 requests doesn't lead to ad revenue either, so here goes:
About a year ago, we bought an Intel-based Xserve with a pair of 80 GB SATA drives to act as our primary Web server. When the boot drive went flaky on us in October 2008, we were able to recover from the backup on the second drive and off-site backups, if a little shakily (see "TidBITS Outage Causes Editors Outrage", 2008-10-07). But although we were able to bring the machine back online, we didn't trust the drive that had failed. Since the Xserve has three drive bays, the obvious solution was to purchase another drive. Sounds simple, doesn't it? Not so much.
You cannot buy a bare hard drive and insert it into an Xserve, as you can with a Mac Pro (and having just added a drive to my new Mac Pro, I can say that Apple did a stunningly nice job in making it easy to add drives, especially in comparison to the awful approach they used in the Power Mac G5). Instead, Xserves require Apple Drive Modules, which are custom carriers containing drives.
For users accustomed to buying inexpensive hard drives, Apple's pricing on the Apple Drive Modules comes as a bit of a shock. An 80 GB SATA ADM costs $200 from Apple, and a 1 TB SATA ADM costs $450. In comparison, a bare 80 GB SATA drive can be purchased for a measly $35, and a 1 TB drive is only about $100. That would seem to point toward buying a new SATA drive and swapping it into the bad drive's ADM. However, when I started down that path, a number of problems arose, such that I bailed on a quick solution and simply purchased a new 80 GB SATA ADM to replace the bad one.
First, I wasn't sure whether my Xserve had SATA drives, as I thought, because System Profiler on the Xserve shows nothing on the SATA bus, instead including all drives on the SAS bus. (SAS stands for Serial Attached SCSI, and is a high-performance data transfer technology that supports fast SCSI drives and is downward compatible with SATA drives.) After some discussion with knowledgeable folks on the MacEnterprise list and careful reading of the drive details in the SAS section of System Profiler, it became clear that both SAS and SATA drives are shown in the SAS section, with SATA drives having "ATA" as the Manufacturer, and showing "Yes" in the SATA Device line.
Second, once I knew that I had SATA drives in my ADMs, I started investigating if there were any gotchas involved in replacing the drives. There turned out to be surprisingly little hard information about this, with some people having replaced an ADM's drive with no trouble and others experiencing performance or reliability issues. I did find a few discussions about how replacing drives isn't recommended, but giving no solid sources.
Confused, I contacted Apple to discuss why ADMs are so expensive in comparison to bare drives, exactly what an ADM does, what Apple recommends users do with failing ADMs, and whether or not replacing a drive in one is a good idea. That conversation revealed a great deal of interesting information about the ADM and shed some light on what people with flaky ADM drives should do.
Drive Selection -- The most important fact to know about ADMs is that Apple doesn't use just any drives. We've all benefited from the amazingly low cost of storage. But whenever manufacturers compete on price, they cut corners every way they can to reduce costs. Although drive reliability is generally good, everyone who buys bare drives regularly has a drive vendor they refuse to patronize due to bad experiences in the past. (As is often the case, these people all hate different vendors, depending on which one was having a bad run at any given time.)
Since the Xserve is designed to be in constant use - 24 hours a day, 7 days a week, for years at a time - Apple doesn't use the least expensive drives available, since those drives are designed for more normal duty cycles in desktop computers - 8 to 10 hours per day, with variable use during that time. Instead, Apple wor
The pixie dust is in the controller, not the platter.
The summary makes it seems that there's no rhyme or reason why Apple charges more for their HDs and why can't the consumer simply replace it with a standard SATA HD. If you RTFA, it goes into a long list of reasons why. Whether you accept Apple's reasoning is another matter.
To begin, XServes use a HD module called ADM rather than simple HDs. On the new MacPros, they also use a module but those modules are designed to replace the HDs inside. For the XServe you apparently can't get a bare drive alone, you have to replace the whole module. The author begins to list the reasons:
And then the author concludes:
Well, there's spam egg sausage and spam, that's not got much spam in it.