[mythtv-users] Mirroring root partition on SSD to a hard drive -- bad idea?

[Gary Buhrmaster]

On Thu, Jan 14, 2016 at 7:27 PM, Eric Ladner <eric.ladner at gmail.com> wrote:
....
> Also, by moving all of /var over, your mysql performnace will not be as high
> as you'd like (it's data files are under /var, right?).  Consider moving
> just /var/log to the HD.  That's where most of the daily churn occurs on
> /var.

The write endurance ratings for most current SSDs suggest
that this is not necessary except in special circumstances
(like you are a Facebook and write the entire capacity every
day).  Sure, MTBF and endurance ratings say nothing about
any particular drive, but they are indicative.

> FWIW,  SSD's fail much more frequently than traditional hard drives.

Citation needed based on much larger sample size than
your anecdotal report.  The (larger scale) numbers from a
few years ago suggest that SSDs fail less than half as often
as HDDs, but as technology changes, so will the failure rates.
So, what research study are you quoting here?

And how cheap were those SSD you purchased?  Not cheap
enough, I would think.  The DC series of SSDs from Intel
(and their enterprise targeted predecessors) have not (yet)
failed me (and yes, if I believed you could tempt fate, I just
did it), and I have lost two (consumer targeted) HDDs during
that period, but that is also just an anecdotal report (for
all I know both of your failures were from P3608 devices).
Consumer devices are, as it has usually been, targeted at
a price point, and not so much a capability point, and you
sometimes do get what you pay for (and sometimes
you just pay more).  In particular, some (especially early
gen) consumer SSD devices have/had failure modes caused
by power failures and the SSD optimizations for improving
(apparent) write speeds.  Many consumer SSD vendors
have improved their firmware or hardware to mitigate that
problem, but not all have (especially the cheapest of the
cheap).


> I agree with Calvin on the backup.

I do agree that mirrors are not a backup.  They are an
availability enhancer.  Mirrors means you get to corrupt
both copies at once.  Which may not be what one wants.