Assuming this predictability is not a good idea in my experience. SSDs fail in various ways, some may be predictable and some are completely unpredictable. It is also not true that an ssd failure means it simply goes to readonly mode. I've seen plenty of SSDs failing unexpectedly and are no longer readable, returning sense key 0x4 (HARDWARE ERROR) and the only recourse is to ship them out.
The risk of correlated failures is indeed non-trivial in SSDs and plain RAID is riskier, be sure to keep a watchful eye on your arrays.
We've currently got about 3500 SSDs in production across our clusters. I worry about them deciding to all fail at once, so far they have been sporadic failures (about 1/2 of which leave the drive unusable).
Are they all the same model?
How long have they been running?
Is it a relatively similar load on all of them?
Can you share smart attributes for them? (in private if needed)
On a very low fire I'm trying to create a disk survey project (http://disksurvey.org ) and such information is of great interest to me.
Good point. I was only addressing the predictability that comes from the flash memory simply wearing out. There are plenty of other ways that drives can fail. But I don't think they introduce any new worries for RAID users the way that flash memory wearing out after so many writes does.
The risk of correlated failures is indeed non-trivial in SSDs and plain RAID is riskier, be sure to keep a watchful eye on your arrays.