[mythtv-users] Can't get storage priorities correctly.

[Stephen Worthington]

On Fri, 17 Nov 2023 22:06:02 -0600, you wrote:

>Thanks for your concern. I thought a  lot before choosing this path.
>
>Yes, I did my calculations. My SSDs have 600TBW and at 30GB per day, I 
>am looking at 54 years of life (600*1000/30/365 ~ 54). I also have 
>smartd doing its thing. It will report when SSDs start using their spare 
>blocks.  At about $60/TB (for 54 years of claimed life), I feel it is a 
>fair game.

That certainly sounds good.  But do check the smartctl -a output - my
new 1 Tbyte SSD in my main MythTV box is only 214 days old, and is
currently showing 16.1 TBytes written without me doing any recording
to it (75 Gbytes per day).  It says it is 1% used, so it is still
going to last a long time, even at that rate.

>So far, in my mythtv usage (10+ years), I have had 10+ spinning disks 
>die. I have still my very first SSD (256G SATA) and several others  as I 
>have no use for them with newer/larger  SSDs replacing the old ones.  
>So, I am looking to try them out to see if TBW values really happen.

Over the last 10 years I think I will have had 10+ hard drives die
also, but only 2 of them prematurely.  The others had been running for
a long time, over their expected lifetime.  I now am buying enterprise
class drives (20+ Tbytes) with 5 year warranties, but they have not
been around for more than 5 years yet.  I do have two ancient
enterprise class 3 Tbyte HGST drives that I swapped out because they
were too small after 9-10 years 24/7.  I put one of them into my
mother's MythTV box running 24/7 again a couple of months later.  It
is currently showing 105553 power on hours (12 years) and is showing
no problems at all.  They were not cheap when I bought them, but they
do show that enterprise class drives can last a very long time.

>Suppose I am wrong and my SSDs show wear, it is a single mythtv-setup 
>change that will get back to trashing spinning disks.

Yes, very easy to do.  I really like how storage groups work.

>When I record and watch at the same time, the amount of seek is very 
>noticeable (especially with RAIDs) and I prefer the random access 
>capabilities of SSDs.

With my enterprise class drives, I can have them recording 2
programmes at once and playing back at the same time with no problems.
From the specifications, I would think three recordings at once would
be fine too, but I never get to that as I have 7 recording drives.  I
can certainly hear them seeking, but it does not sound over the top at
all.  But I can also do 2 recordings plus playback from my old (very
quiet) WD Green 4 Tbyte drives, which have much lower specifications.
They are currently showing 81029 and 77591 power on hours (9.2 and 8.9
years).  So even cheap drives can last well if you get lucky and they
were over designed.

I am wondering if RAID 1 is the problem somehow.  If the data was
being written to the first drive and then read back again to be copied
to the second drive, that might cause what you are getting.  But that
would be a really bad way of doing RAID 1 when you can just write to
both drives at once from the same buffers.

>Regards
>Ramesh