[mythtv-users] new drive won't boot

Stephen Worthington stephen_agent at jsw.gen.nz
Fri Dec 21 05:03:45 UTC 2018


On Fri, 21 Dec 2018 11:50:46 +0800, you wrote:

>Lots below if you want to go there!
>
>> No, it a myth that SSDs wear out rapidly.  Modern SSDs have much more
>> endurance. 
>
>According to all the info I can find modern disks wear out FASTER than older disks. The thing that makes this seem not true is smaller disks wearout faster than large disks. EG the Samsung EVO 850 is rated for a total write of 600TB (The pro 1200TB) but the actual cell write life is down to 3000! 
>https://www.compuram.de/blog/en/the-life-span-of-a-ssd-how-long-does-it-last-and-what-can-be-done-to-take-care/
>
>> Here are is the real life SMART data from two of my SSDs:
>
>Stephen that is most interesting thank you. It directly contradicts my own experience.
>I had an 850 EVO 256G as my main disk.
>Partitioned (EFI, swap) 20G /, and 200G /store (for myth) with 50G un-provisioned
>
>After a year the disk became read-only, SMART said interesting stuff (long lost) and it took GREAT PAIN to reconfig another disk.
>This SSD had NO writable sectors left (I must consider that the disk failed)
>
>It is worth trying again (what I’m trying to fix is if I watch a show WHILE it is recording every few seconds playback pauses for a fraction of a second, initially not noticable but eventually quite irritating. 
>If I watch a recording while something else is recording the problem does not occur) IE usb and tuners not the problem.
>
>I’m running fixes/29 [v29.1-15-g280138b452] which I compiled myself as I fiddled with lots of debug stuff while I was trying to resolve the meta data saga.
>
>James 

You should have been able to get the SMART data from the 850 EVO to
tell what its problem was.  But if it died in less than a year and the
SMART data did not say you had written more Tbytes than it was rated
for, then it would be a warranty replacement - just a disk that failed
early, as does happen to a percentage of all disks.

Doing recordings to an SSD is something that you would have to
calculate carefully.  Each recording from an HD channel here in New
Zealand is in the range of 3-7 Gibytes per hour.  So that amount of
writing to the SSD would add up rapidly if you were recording several
programmes a day.  When I was looking at getting my NVMe SSD, I did
all those calculations and decided that it was not a good idea to put
the recordings on the SSD, except for a short time in an emergency.  I
had been wondering if I could use just one or two huge hard drives for
storing recordings, with the recordings being done on the SSD and then
moved to hard disk afterwards.  But the calculations said that would
be a very bad idea - if I remember correctly, the SSD would only have
lasted for less than a year.  So I kept my seven rotating rust
recording drives so that I would be able to record as much as I wanted
directly to them.

Your problem with pauses while watching live from a recording is
likely the same one that you get with watching using Live TV.  MythTV
does not calculate correctly how much buffer it needs to prevent the
pauses, so if you are playing back from too close to what is being
recorded, it runs out of buffered data and has to wait for more to
arrive from the tuner.  The solution is simple - just pause for a few
seconds, then resume watching.  It means you are watching a few
seconds further back from real time, but you are already doing that
anyway as MythTV always plays back from data that has already been
sent to the disk, not from the stream arriving from the tuner.  If you
want to watch as close to real time as possible, you need to do that
with something that is directly connected to its tuner, such as a TV.
But even then, with digital TV systems all the digital processing at
the transmitter and at the receiver still means that you will be
seeing things a second or two behind real time, and behind what you
would have been seeing with the old analogue TV systems.


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