Big Sur slow with external RAID 5 box.

I have an i7 Mac Mini running Big Sur, and an external Raidon box (RAID 5, 4x2TB) connected via an eSATA/USB3 adapter.

The Mac's internal SSD holds the OS, application folders, and my user folder. On the RAID are several partitions, one of which is for Time Machine, one for big static files like movies and photos, and one of which contains folders for which I have aliases in my user folder.

Often, the Mac hangs up (spinning beach ball) while the RAID drives are spun up one by one, for no apparent reason, when I try to launch an app, or open a file (even if the file is on the internal SSD.) Time Machine is not active, and when Spotlight indexing is in progress, all four drives are busy simultaneously. This seems to be the OS waking the array, but I can't imagine why it wants to. It's only about 30 seconds of delay, but it's pretty freaking annoying. Anybody have any idea what's up, and how I might prevent it?

Posted on May 19, 2021 12:45 PM

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jpdemers Author

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144 points

Posted on Jun 21, 2021 3:46 AM

RAID box is self-contained; I have no software controller for it. It's just plug-and-play, appearing as a single drive to Disk Utility. Evidently it does not employ caching.

I solved the problem by installing the freeware app "Keep Drive Spinning", which prevents drives from spinning down. Minor downside is the bit of added power consumption, but it takes very little juice to keep a drive spinning. I have enterprise-level drives in the box (Hitachi server class, designed to run 24/7) so no worries there.

Curious that I had no issues prior to installing Big Sur. Apple monkeyed around with the external storage I/O, and not in a good way. Mac OS these days just ASSUMES that all drives are SSDs, which is a poor approach to real-world users (like moi) who can't afford multiple terabytes of solid state storage.

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Big Sur slow with external RAID 5 box.

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