[mythtv-users] Putting Myth's DB on an SD card / SSD?

Robin Hill myth at robinhill.me.uk
Thu Nov 17 18:24:30 UTC 2011

On Thu Nov 17, 2011 at 12:54:55 -0500, Mark Lord wrote:

> On 11-11-17 12:48 AM, Tyler T wrote:
> > In order to improve WAF I'm going to be adding a second ATSC (OTA)
> > tuner to my Myth system. Right now, I've got my OS, DB, and recordings
> > all on a 2.5" USB hard drive and I'm going to go ahead and assume that
> > watching one, and recording two, HD streams all at once is going to
> > cause issues. So:
> > 
> > Is any random SD card going to have write performance fast enough to
> > host Myth's seektables, or should I go shopping for one with
> > "upgraded" write performance? In a non-scientific test, I seem to get
> > about 5MB/s write speed on an old 1GB SD card I already have. That may
> > sound slow but really, during a recording Myth isn't writing megs to
> > the DB (just lots and lots of tiny writes). I don't care if
> > mythfilldatabase or reschedules are slow.
> Mmm.. good questions.  I was wondering about this too,
> and it's easy enough to experiment with.
> I've got a "Class 10" SD card to try it with,
> so perhaps I'll just give it a whirl and see what happens.
> If the DB works well enough on the SDcard,
> then why not the entire root filesystem there as well?
I'm not sure a class 10 card is best fitted for that usage. In order to
get the high-throughput required for class 10 qualification, there's all
sorts of pre-allocation going on behind the scenes. A database isn't
doing high-throughput streaming, but random small I/O, so won't be
getting the benefit from the class 10 device (and may even be running
into issues - I certainly know of corruption issues with class 10
microSD cards on mobile phones, but that may be just due to conflicts
with power-saving modes).

SD cards are not the same as SSDs and don't have anywhere near as
sophisticated wear leveling techniques. Having said that, people have
been using CF cards for a long time without serious issues having been
reported. Performance-wise, I'd expect most SD cards would be okay - as
said, database reads/writes are pretty low, and high random-access
speeds are going to be more important than throughput,

All the wear-leveling is done in the background, so the filesystem isn't
too critical. Make sure you use noatime though, to reduce unnecessary

    ( ' }     |       Robin Hill        <myth at robinhill.me.uk>  |
   / / )      | Little Jim says ....                            |
  // !!       |      "He fallen in de water !!"                 |
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