Generally, since I began using ZEVO, I have sensed deep trouble very rarely.
Two recent incidents
All of the following were true:
- in System Preferences, hard disks were allowed to sleep
- the Mac was allowed to sleep (after maybe fifteen minutes)
- a vdev is formed of multiple devices (I have experimented with no more than two)
- both devices are on a hub (I recently purchased a new one, USB 2.0).
In my case both disk devices are almost certainly good – very recently scrubbed, never an error before trouble began.
Less recently
I don't always trust my MacBookPro5,2 to achieve – with combinations of external third party hardware and firmware – what's preferred in the Energy Saver pane of System Preferences.
An example: with certain disks in a dock on USB, I could use the disk for only as long as reads (or writes) were close to non-stop. After a minor break in activity, I'd 'lose' the disk as if a bus or I/O error had occurred (the volume remained in Finder but I could no longer get folder contents whilst browsing, and so on). Whether those problems were hard disk drive sleep-related I don't know, but simply: something wasn't right.
Determining whether a disk is active, idle or sleeping
Wish for something like SpindownHD (described in an answer to hdparm on OS X).
Any suggestions, people?
Generally
In the quick start guide for ZEVO Community Edition 1.1 there's no caution against USB. So whilst I appreciate that USB (2.0 in particular) can be troublesome – troublesome not only for ZFS – I lean strongly towards:
- disallowing sleep to minimise the risk of trouble.