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

[Calvin Dodge]

I'm curious, Eric - did you have any warnings of SSD failures, like
"smart" information related to wear leveling?  What brands of SSDs
have you used? Did they fail under normal circumstances, or after an
unexpected power off event?


For backups I do something like this, because it lets me keep multiple
old version of files.

1) designate an archive location
2) Every day, make a copy of files in that location with "cp -al" (the
-l means "make hard links of files, rather than copying them) to a new
directory (my script creates on named YYYYMMDD). For me the location
is /backups, with the rsync directory (see step 3) being
/backups/latest, with daily directories like /backups/20160101,
/backups/20160102, etc.
3) rsync -a --delete source to destination. Since any files will be
deleted and replaced, rather than changed, the old versions of such
files will be safe in those daily directories.

Calvin

On Thu, Jan 14, 2016 at 1:27 PM, Eric Ladner <eric.ladner at gmail.com> wrote:
> Mirroring with one side on an SSD and the other on a regular HD will reduce
> your write performance significantly (and possibly read performance if some
> percentage of reads are forwarded to the HD).
>
> 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.
>
> FWIW,  SSD's fail much more frequently than traditional hard drives.  I've
> got hard drives that are 6 and 8 years old.  I've never had an SSD last more
> than three years.  And be warned, when an SSD fails, it fails hard.  Not
> like a regular hard drive where you can limp along and get some stuff off as
> it's dying.  With an SSD failure (or the three I've had fail so far) one
> minute it's working, the next minute it's a 2.5 inch wide paper weight.
>
> I agree with Calvin on the backup.   Copy it to a backup folder on the HD
> and rsync it over once a day or once a week.  Be mindful that you'll be
> backing up an open database.   Run a database dump prior to the rsync (or
> backup method of your choice).
>
> Eric
>
> On Thu, Jan 14, 2016 at 10:12 AM Calvin Dodge <caldodge at gmail.com> wrote:
>>
>> I think the hard drive is more likely to fail than the SSD. I think
>> you'd be better off doing a one-time backup to a hard drive, then
>> incremental backups.
>>
>> Calvin Dodge
>>
>> On Thu, Jan 14, 2016 at 9:48 AM, Craig Huff <huffcslists at gmail.com> wrote:
>> > I have migrated my system disk to an SSD with /var mounted on a separate
>> > hard drive to limit wear on the SSD. For protection against the day the
>> > SSD
>> > fails, I'm thinking of mirroring it to a partition on an available hard
>> > drive.  It appears I can do this with either the traditional software
>> > raid
>> > approach using mdadm that looks a lot like what I did with Sun Solaris
>> > systems many years ago, or with dmraid, taking advantage of the Intel
>> > hardware (firmware?) support on my motherboard, although that may be an
>> > issue with the SSD on a SATA 3.0 port and the hard drive on a SATA 2.0
>> > port.
>> > If I go ahead, I'll have to investigate that.
>> >
>> > As complicated as setting up and maintaining this system has been, I'm
>> > of
>> > mixed opinions on whether this would just be another step in the process
>> > or
>> > the straw that breaks the camel's back.
>> >
>> > I'd appreciate any advice or opinions.
>> >
>> > --
>> > Craig.
>> >
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