Hi Peter,
I think you must be referring to this section in the ZFS admin guide:
http://docs.sun.com/app/docs/doc/819-5461/6n7ht6qrr?a=view
If you are creating a RAID-Z configuration with many disks, as in this
example, a RAID-Z configuration with 14 disks is better split into a two
7-disk groupings. RAID-Z configurations with single-digit groupings of
disks should perform better.
This is a general recommendation about performance of RAID and not a
comment about disk failure probabilities.
If this isn't the text that is causing you grief, please let me know and
I'll fix that one.
Maintaining a balance in the admin guide between providing ZFS features
and examples and a kitchen sink of everything you wanted to know or do
with ZFS is a difficult task. :-)
I hope to include more links to blogs and our developing ZFS best
practices site in the Admin Guide to provide more practical
recommendations based on what you want to do with ZFS.
http://www.solarisinternals.com/wiki/index.php/ZFS_Best_Practices_Guide
Cindy
Peter Schuller wrote:
PS> The ZFS administration guide mentions this recommendation, but does not
give PS> any hint as to why. A reader may assume/believe it's just general
adviced, PS> based on someone's opinion that with more than 9 drives, the
statistical PS> probability of failure is too high for raidz (or raid5).
It's a shame the PS> statement in the guide is not further qualified to
actually explain that PS> there is a concrete issue at play.
I don't know if ZFS MAN pages should teach people about RAID.
If somebody doesn't understand RAID basics then some kind of tool
where you just specify pool of disk and have to choose from: space
efficient, performance, non-redundant and that's it - all the rest
will be hidden.
But the guide *does* make a recommendation, but does not qualify it. And if
there is a problem specific to ZFS that is NOT just obvious results of some
general principle, that's very relevant for the ZFS administration guide IMO
(and man pages for that matter).
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