[mythtv-users] Anyone using Seagate 8T (ST8000AS0002) Hard Drives?

[Stephen Worthington]

On Wed, 9 Mar 2016 10:45:51 +0000, you wrote:

>Yes, I have two of these, one for archiving videos, and one for
>> archiving recordings.  It would not be a good idea to use one for
>> recording directly to, as the write speed goes down to virtually zero
>> at times when it is doing its SMR re-writing.  My recording drive is
>> simply put in a new storagegroup I created called "Archives".  Any
>> recordings moved to this drive are able to be played and deleted
>> without problems, but it will never be recorded to unless I change a
>> recording rule to specifically refer to that drive.
>>
>
>I've been using one of these SMR drives for several months.  I initially
>had some concerns about recording directly to the drive, but after testing
>it a bit, it hasn't been an issue in practice.  The drive itself has a good
>amount of "write cache" space (around 20GB or so) which it can write to
>without the problematic read-modify-write cycles.  As long as your
>recordings don't exceed that cache space, and you have downtime (overnight,
>between recordings, etc.) to allow the drive to migrate the data out of the
>cache, it isn't really an issue.
>
>The safest way to handle them is probably what has already been mentioned,
>which is to move/archive things to the drive manually.  However, I haven't
>run into any trouble as of yet with a moderate amount of recording
>happening directly to the drive.  I'm running on a vanilla 3.16.1 kernel
>and haven't had any operating system issues with the drive, so as long as
>you avoid the older kernels you should be fine.
>
>--Dave

No, it is the newer kernels you have to avoid.  Older kernels do not
know about SMR drives and just assume they are normal drives, which
works fine for the ST8000AS0002 drives which are "drive managed" -
they do all the special SMR operations on the shingles themselves in
the drive controller.  Other SMR drives are "system managed" and
require special SMR drivers to work at all, as the system has to do
the shingle rewriting.  So newer kernels introduced drivers that
recognise SMR drives and attempt to do the right things for them.  But
for the ST8000AS0002 drives, they are buggy and timeout when an SMR
rewrite of a shingle happens.  The older drivers that do not know
about SMR drives have a very long timeout that allows the rewrite
operation to complete without the kernel interfering.

When first filling up an ST8000AS0002 drive, virtually no rewrites
happen as the filesystem's directory information that gets rewritten
all the time just happens to be in the area at the start of the drive
that is not shingled.  But once you have deleted files and then add
new ones, you start to get shingle rewrites and the problems will
happen with the new drivers.

See here: https://bbs.archlinux.org/viewtopic.php?id=199351