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Hibernate Mode With OWC SSDs, and All Sandforce-based SSDs

“Doctor, it hurts when I do that!”
Doctor: Don’t do that!

There is an outstanding issue (now resolved) with OWC solid state drives and any Sandforce-based SSD when Hibernate mode is invoked on a Mac: the Mac won’t wake up properly if forced into Hibernate mode.

Hibernate is NOT sleep mode, it is an entirely different mode in which the entire contents of memory are written to a huge file on disk. Force Hibernate mode off as described further below.

The Hibernate issue has caused some consternation with a few Mac users that have deliberately (or perhaps inadvertently) activated the use of Hibernate mode. The conspiracy theorists have their panties in a bundle over this. It only came to my attention in the past few weeks, and I did not have enough data to understand the issue until recently.

Hibernate mode

Hibernate mode is not sleep mode, and I am unaware of any other sleep-like issue with OWC SSDs. The issue is (was) a Sandforce firmware issue, and is (was) not specific to OWC SSDs, it applies to any brand with the Sandforce controller.

  • Apple does not support Hibernate mode on any Macs except the MacBook and MacBook Pro, and even on the MacBook Pro, Hibernate mode is invoked only when the battery is about to be drained (a few percent remaining).
  • Hibernate mode is not supported on the Mac Pro, iMac, MacMini, or even the MacBook Air (though MBAir uses a very similar Standby mode, and no know issues with OWC SSDs there).
  • There is some possibility that Apple’s Migration Assistant sets Hibernate mode on non-laptop systems when transferring data— a bug.
  • You can force on Hibernate mode and cause yourself grief.
  • Hibernate mode sucks up disk space equivalent to the amount of memory, e.g., 8GB on a MacBook Pro with 8GB memory, 16GB on a MBP with 16GB memory. That’s a lot if you have a small SSD where space is limited, and it takes a relatively long time to write that file when entering Hibernate mode.

Current status of OWC SSDs

This is the information that I have from OWC:

  • A Sandforce firmware update addresses the Hibernate issue, OWC has just finished validating and tested the new firmware, and all OWC SSDs that are now shipping as of March 18, 2011 now have the latest firmware.
  • At present, SSDs in the field can update their firmware with a Windows-based updater. OWC has a Mac updater in progress but it’s not available quite yet.

My six OWC SSDs have worked perfectly

Over the past year, I bought and installed six OWC SSDs in four different Macs: two Mac Pros and two MacBook Pros. Most of these have been in use nearly a year now, with zero sleep issues. I sleep my Mac Pro with its triple-SSD RAID-0 stripe multiple times per day.

I am unable to reproduce any sleep issue on my Macs, presumably because there isn’t any sleep issue. To wit, I have not gone and forced my Mac Pro into an unsupported mode to invent a problem. Nor have I had any issues with my MacBook Pros, though presumably it would occur when and if the battery were nearly fully drained.

Forcing Hibernate mode off

See How to Delete a Space-Hogging Sleep File sleepimage for details on forcing Hibernate mode to be off. Be sure to read the warnings.

User disputes my statements about Hibernate

I’m not always right, but I verify my statements whenever possible.

One user wrote me, chastising me for some of my points, because he read a manual page that apparently contradicts my statements (“You can verify that for yourself by reading the pmset man page”. It’s written, therefore reality must conform to the printed word? I prefer to test and see what actually happens.

What actually happens with Hibernate mode (as stated above in my original post):
1) regular sleep mode is entered
2) Only if the battery power drops too low, the memory is written to disk.

I verified this by booting off an external hard drive (relatively slow). I ensured that there was 6.4GB of constantly changing memory to be written to disk (by using MemoryTester 'stress'). Invoking the Sleep menu command, I observed that there was minimal disk activity, then everything shut off within about 5 seconds, including the hard drive. Hence memory was never written to disk, because it should take at least 60 seconds to write 6.4GB of memory to disk. This simply does not happen. Therefore, Hibernate mode is all about writing to disk when the battery actually runs low.

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