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SMR drives on Mythtv
Does anyone have an opinion on SMR type drives for PVR applications such
as myth? Newegg has a really good deal on 4TB Seagate SMR drives for
$89 right now.
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Re: SMR drives on Mythtv [ In reply to ]
On Tue, 30 Jan 2018 22:32:17 -0500, you wrote:

>Does anyone have an opinion on SMR type drives for PVR applications such
>as myth? Newegg has a really good deal on 4TB Seagate SMR drives for
>$89 right now.

As far as I know, the smallest shingled drive that Seagate makes is 8
Tbytes. Do you have a URL for the Newegg ones? It is likely that
Newegg is mislabeling them as SMR when they are actually normal
drives. You need to look up the model number on Seagate's web site
and download its data sheet to find out.

Shingled drives are unsuitable for recording to, as when they have to
do a shingle re-write, they can stop accepting write data for a long
period - many seconds. The MythTV recording buffers and operating
system write buffers are nowhere near big enough to buffer that much
data and will overflow, resulting in lost data in the middle of the
recording.

However, you can use SMR drives as storage for recordings - I have
four Seagate ST8000AS0002 (8 Tbyte) drives that I use that way.
Recordings go to my seven non-shingled recording drives, and the
recording files can be copied off to the SMR drives once recording is
completed. I wrote myself some Python to automate the process of
selecting the oldest recordings and moving them to the SMR drives,
which I have in an "archive" storagegroup so that MythTV can see all
the recording files. But as I do not have any recording rules that
will record to the archive storagegroup, those drive are never used
for recording to.
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Re: SMR drives on Mythtv [ In reply to ]
On 31/01/18 06:44, Stephen Worthington wrote:

> However, you can use SMR drives as storage for recordings - I have
> four Seagate ST8000AS0002 (8 Tbyte) drives that I use that way.
> Recordings go to my seven non-shingled recording drives, and the
> recording files can be copied off to the SMR drives once recording is
> completed. I wrote myself some Python to automate the process of
> selecting the oldest recordings and moving them to the SMR drives,
> which I have in an "archive" storagegroup so that MythTV can see all
> the recording files. But as I do not have any recording rules that
> will record to the archive storagegroup, those drive are never used
> for recording to.

A query about this: do you have seektables for the archive SG? If so,
no wonder you need to watch free space on the partition used by
optimize_mythdb - and it must impede other DB access for quite long
periods. Is there a transcode-free, seektable-free format that would
still allow seeking, and can Mythfrontend use it?

John P


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Re: SMR drives on Mythtv [ In reply to ]
On Wed, 31 Jan 2018 10:04:54 +0000, you wrote:

>On 31/01/18 06:44, Stephen Worthington wrote:
>
>> However, you can use SMR drives as storage for recordings - I have
>> four Seagate ST8000AS0002 (8 Tbyte) drives that I use that way.
>> Recordings go to my seven non-shingled recording drives, and the
>> recording files can be copied off to the SMR drives once recording is
>> completed. I wrote myself some Python to automate the process of
>> selecting the oldest recordings and moving them to the SMR drives,
>> which I have in an "archive" storagegroup so that MythTV can see all
>> the recording files. But as I do not have any recording rules that
>> will record to the archive storagegroup, those drive are never used
>> for recording to.
>
>A query about this: do you have seektables for the archive SG? If so,
>no wonder you need to watch free space on the partition used by
>optimize_mythdb - and it must impede other DB access for quite long
>periods. Is there a transcode-free, seektable-free format that would
>still allow seeking, and can Mythfrontend use it?
>
>John P

In any normal MythTV database, for any recording in the database there
will be recordedseek entries. Moving the recording files to different
locations or to different storagegroups does not change that - it does
not actually have any affect whatsoever on the database. So yes, all
the recordings on my archive storagegroup drives have normal
recordedseek entries. So as I have a large number of recordings, my
recordedseek table is correspondingly huge:

MariaDB [mythconverg]> select count(*) from recorded;
+----------+
| count(*) |
+----------+
| 25907 |
+----------+
1 row in set (0.00 sec)

MariaDB [mythconverg]> select count(*) from recordedseek;
+-----------+
| count(*) |
+-----------+
| 241096367 |
+-----------+
1 row in set (0.00 sec)

root@mypvr:/var/lib/mysql/mythconverg# ll recordedseek.*
-rw-rw---- 1 mysql mysql 1041 Jan 19 07:37 recordedseek.frm
-rw-rw---- 1 mysql mysql 6028544575 Feb 1 01:04 recordedseek.MYD
-rw-rw---- 1 mysql mysql 5517818880 Feb 1 01:04 recordedseek.MYI
root@mypvr:/var/lib/mysql/mythconverg# ll -h recordedseek.*
-rw-rw---- 1 mysql mysql 1.1K Jan 19 07:37 recordedseek.frm
-rw-rw---- 1 mysql mysql 5.7G Feb 1 01:04 recordedseek.MYD
-rw-rw---- 1 mysql mysql 5.2G Feb 1 01:04 recordedseek.MYI

My database is on the system partition, which is a 100 Gibyte
partition of a very fast NVMe SSD (Samsung 950 Pro - 256 Gbyte). Even
with that assistance, the size of recordedseek means that it takes a
long time to optimise or to backup. Before I moved the system to that
SSD, that used to cause problems if a recording was happening at the
same time. But now the normal MySQL system of journaling the updates
to a table that is being optimised allows recordings to happen without
problems at the same time. The journal is used to update the
recordedseek table after the optimise completes. The NVMe SSD has
enough random I/O capacity to handle the normal database accesses and
updates at the same time as the optimise or backup. My old spinning
rust system drive (an excellent Hitachi HDS723030ALA640 3 Tbyte) could
not manage that, probably due to too much head movement being
required.

Without a seek table, DVB-T and DVB-S recordings in MPEG-2 transport
stream format as we have here in New Zealand all seem to be OK for
seeking - it takes a bit longer, and is probably not as accurate, but
it functions well enough for most purposes such as skipping ad breaks.
If the seek table is deleted for a recording, it can be regenerated
using mythcommflag --rebuild or mythutil --checkrecordings
--fixseektable. For my DVB-T and DVB-S recordings, it takes a few
minutes per recording to do the regeneration.
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Re: SMR drives on Mythtv [ In reply to ]
On 01/31/2018 01:44 AM, Stephen Worthington wrote:
> On Tue, 30 Jan 2018 22:32:17 -0500, you wrote:
>
>> Does anyone have an opinion on SMR type drives for PVR applications such
>> as myth? Newegg has a really good deal on 4TB Seagate SMR drives for
>> $89 right now.
> As far as I know, the smallest shingled drive that Seagate makes is 8
> Tbytes. Do you have a URL for the Newegg ones?

I think he's talking about the Seagate ST4000DM004 at:

https://www.newegg.com/Product/Product.aspx?Item=N82E16822179299

which is $99.99, but until 11:59PM PST on Feb 1 (Mid-Winter Savings
Blitz Deal) is available for $89.99 with promo code EMCXPESP2

> It is likely that
> Newegg is mislabeling them as SMR when they are actually normal
> drives.

I'm pretty sure Newegg isn't labeling them as SMR, however comments on
the internet are rife with claims that it's an SMR drive.

> You need to look up the model number on Seagate's web site
> and download its data sheet to find out.

It doesn't seem to say:

Data Sheet:
https://www.seagate.com/www-content/datasheets/pdfs/3-5-barracuda-3tbDS1900-9-1710US-en_US.pdf
Manual:
https://www.seagate.com/www-content/product-content/barracuda-fam/barracuda-new/en-us/docs/100805918g.pdf

(both from
https://www.seagate.com/internal-hard-drives/hdd/barracuda/?sku=ST4000DM004#specs-3-5
, along with data sheets/manuals for similar models)

It's in the same family as the ST8000DM004 (8TB), which I'm pretty sure
is a shingled drive, but also the ST2000DM002/DM006 (2TB models) and
even a 1TB and 500GB model--that wouldn't make sense to be shingled...
It's very thin (fewer platters than my ST4000DM001, the
earlier-generation model). I know because I just finished installing
one (that I bought for $9 more than the sale price on Amazon the day
before Newegg started the sale)--I needed a quick replacement for a
drive that was about to fail.

If anyone knows if it is shingled, I'd love to know so I can convert it
to a MythTV archive disk. Or, if there are any hdparm or smartctl or
whatever commands or logging information I can use to find out, please
let me know and I'll check.

Thanks,
Mike
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Re: SMR drives on Mythtv [ In reply to ]
According to the Seagate datasheet[1], these are TGMR (Tunneling Giant Magneto-Resistive) head drives not SMR. It's a high density variant of PMR that Seagate brought out circa 2011. I have several of the 2TB and 4TB variants of these drives running and they are very good with sustained writes as you would see while recording in myth.

[1] https://www.seagate.com/www-content/product-content/barracuda-fam/barracuda-new/en-us/docs/100805918d.pdf

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Re: SMR drives on Mythtv [ In reply to ]
On 31/01/18 19:43, Shawn Flynn wrote:
> According to the Seagate datasheet[1], these are TGMR (Tunneling Giant Magneto-Resistive) head drives not SMR. It's a high density variant of PMR that Seagate brought out circa 2011. I have several of the 2TB and 4TB variants of these drives running and they are very good with sustained writes as you would see while recording in myth.
>
> [1] https://www.seagate.com/www-content/product-content/barracuda-fam/barracuda-new/en-us/docs/100805918d.pdf
>

FWIW: The discoverers of the effect behind this technology got the
physics Nobel prize 2007.

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Re: SMR drives on Mythtv [ In reply to ]
On 01/31/2018 02:43 PM, Shawn Flynn wrote:
> According to the Seagate datasheet[1], these are TGMR (Tunneling Giant Magneto-Resistive) head drives not SMR. It's a high density variant of PMR that Seagate brought out circa 2011. I have several of the 2TB and 4TB variants of these drives running and they are very good with sustained writes as you would see while recording in myth.
>
> [1] https://www.seagate.com/www-content/product-content/barracuda-fam/barracuda-new/en-us/docs/100805918d.pdf

Good to know. I knew it was TGMR, but didn't know if that was mutually
exclusive with SMR. I didn't know if TGMR was a lower-level recording
method which can be shingled or not shingled. Does that mean that SMR
uses SMR-specific recording heads, and any other recording method
specified is not shingled?

Mike
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Re: SMR drives on Mythtv [ In reply to ]
Michael T. Dean <mtdean@thirdcontact.com> wrote:

> Does that mean that SMR uses SMR-specific recording heads, and any other recording method specified is not shingled?

The key thing about shingled drives is that they can make use of the physics that makes it possible to have a read head that works with a narrower track than the write head. So you write the narrowest track that you can make a head for, but instead of leaving a guard zone and then writing another track - you write the next track so it overlaps the first one, leaving a narrower track which is all that's needed for the read head.

The problem is that you can't re-write anything but the last track in the group* - so you have to re-write the whole track group if you change any part of it. This typically means reading the whole track group, updating (in the buffer) the sectors you've changed, and then writing it out again - normally to different track group on the disk (so you still have the original if the power fails mid operation).

It is this "read a load of data; write it out again" that makes these drives stop processing requests for seconds at a time - they are having to move a chunk of data about internally.

* Obviously it would be impractical if you had to re-write the whole disk, so there are multiple zones with guard zones between them.
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Re: SMR drives on Mythtv [ In reply to ]
On Wed, 31 Jan 2018 13:53:48 -0500, you wrote:

>On 01/31/2018 01:44 AM, Stephen Worthington wrote:
>> On Tue, 30 Jan 2018 22:32:17 -0500, you wrote:
>>
>>> Does anyone have an opinion on SMR type drives for PVR applications such
>>> as myth? Newegg has a really good deal on 4TB Seagate SMR drives for
>>> $89 right now.
>> As far as I know, the smallest shingled drive that Seagate makes is 8
>> Tbytes. Do you have a URL for the Newegg ones?
>
>I think he's talking about the Seagate ST4000DM004 at:
>
>https://www.newegg.com/Product/Product.aspx?Item=N82E16822179299
>
>which is $99.99, but until 11:59PM PST on Feb 1 (Mid-Winter Savings
>Blitz Deal) is available for $89.99 with promo code EMCXPESP2
>
>> It is likely that
>> Newegg is mislabeling them as SMR when they are actually normal
>> drives.
>
>I'm pretty sure Newegg isn't labeling them as SMR, however comments on
>the internet are rife with claims that it's an SMR drive.
>
>> You need to look up the model number on Seagate's web site
>> and download its data sheet to find out.
>
>It doesn't seem to say:
>
>Data Sheet:
>https://www.seagate.com/www-content/datasheets/pdfs/3-5-barracuda-3tbDS1900-9-1710US-en_US.pdf
>Manual:
>https://www.seagate.com/www-content/product-content/barracuda-fam/barracuda-new/en-us/docs/100805918g.pdf
>
>(both from
>https://www.seagate.com/internal-hard-drives/hdd/barracuda/?sku=ST4000DM004#specs-3-5
>, along with data sheets/manuals for similar models)
>
>It's in the same family as the ST8000DM004 (8TB), which I'm pretty sure
>is a shingled drive, but also the ST2000DM002/DM006 (2TB models) and
>even a 1TB and 500GB model--that wouldn't make sense to be shingled...
>It's very thin (fewer platters than my ST4000DM001, the
>earlier-generation model). I know because I just finished installing
>one (that I bought for $9 more than the sale price on Amazon the day
>before Newegg started the sale)--I needed a quick replacement for a
>drive that was about to fail.
>
>If anyone knows if it is shingled, I'd love to know so I can convert it
>to a MythTV archive disk. Or, if there are any hdparm or smartctl or
>whatever commands or logging information I can use to find out, please
>let me know and I'll check.
>
>Thanks,
>Mike

No, none of the STx000DM00y drives are shingled. The shingled drives
are AS model, not DM. The manual from Seagate's site does not mention
the word "shingle" or "SMR" anywhere. This is a case of someone on
the net making wrong conclusions about a product and others
propagating them without actually checking the facts. The DM series
drives are normal desktop drives and should be fine for recording.
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Re: SMR drives on Mythtv [ In reply to ]
"Michael T. Dean" <mtdean@thirdcontact.com> writes:

<snip>
> earlier-generation model). I know because I just finished installing
> one (that I bought for $9 more than the sale price on Amazon the day
> before Newegg started the sale)--I needed a quick replacement for a
> drive that was about to fail.

You can contact Amazon customer service. They have been good to me about
pretty good about matching prices in similar circumstances.

Leo

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