On Sat, 03 Feb 2018 21:46:42 +0000 "Digby R.S. Tarvin" <digby...@gmail.com> 
wrote:
Digby R.S. Tarvin writes:
> 
>  Thats why I described my use case - to make the MTBF figures meaningful.  As
> I said, I have my system configured so that most heavy write accesses go to
> rotating media. I typically try to have my system partitions mounted read
> only, except var and tmp. I am currently using 32GB uSD devices for
> raspberry pi based servers, with about 100GB per year in writes (as
> reported by iostat), plus perhaps an initial 100GB in writing that occurs
> during installation and configuring. The last failure I had was about 3
> months ago, on uSD card that had been in use for just under 2 years.
>
> I can only speak of the experience that I have had, but I don't think my
> usage is sufficiently atypical to not count as 'in practice' for use as
> computer storage (ie I am not talking about  music players and cameras,
> phones etc).

Note that consumer grade uSD cards are much worse than SSDs --
they are mainly for the video recording market where capacity
is more important.  Not to mention The RasPis are poor at
reliability.  Even a xenon flash or near a RasPi could power a
RasPi2 down! And since they do no onboard power regulation,
people had lots of problems early on -- add one more USB
device and the thing can become unreliable.

At 100GB per year the SSD I am talking about should
last 3000 years!

Newer *high endurance* SanDisk microSDXC cards for example can
do 10k hours of video recording at a rate of 26Mbps speed.
That translates to about 117TBW. At 100GB writes/year they
should last over 1000 years.

> So from my experience, I would still tend to go along with Erik's advice
> (as relayed by Steve), or perhaps be even more fastidious about backups
> when using flash...

I think this has shifted more in favor of SSDs in the past
couple years.

The convention wisdom for ZFS was to not use SSDs for its
intent log (as all writes go through it) but it was okay to
use SSDs for the read cache, L2ARC (though that may not be
very effective). This is similar to Erik's recommendation.
But this falls apart if you use SSDs as your main storage.

To use a 300TBW device for 10 years, you'd have to *average*
over 82GB a day per device. I certainly don't see traffic
anywhere near that. If it weren't for the cost, I would
rebuilt my zfs array using SSDs. [Note that ZFS does its own
checksumming and has redundancy of its own]

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