[mythtv-users] Building a new MythTV Backend for 2022

[James]

> On 9 Jan 2022, at 8:57 pm, Jim Abernathy <jfabernathy at gmail.com> wrote:
> 
> 
> On 1/9/22 12:49 AM, Mark Wedel wrote:
>> On 1/8/22 8:39 AM, James Abernathy wrote:
>>> With v32 coming soon, I'm looking at an upgrade of not only the software, but maybe it's time for the 11 year old hardware to be retired.  So I'm looking for thoughts on that.
>>> 
>>> My current system has an SSD boot drive and 4 SATA II hard drives configured as 2 mirrors. Since they were SATA II at the time, I thought that for performance reasons, I needed 2 directories in my Recording Storage Group so the recordings would be split between mirrors.  Not sure how needed that was, but it's been working well for 10 years or so.  A secondary use of the backend is as a SMB/CIFS NAS for the rest of the house to use.
>>> 
>>> Since NAS drives are reasonably priced now, I thought about a pair of Seagate Ironwolf 4TB SATA III drives used in a mirrored configuration.
>>> 
>>> So one question is can I forget the use of a second directory in my Default Storage Group (recordings)?  My tuner is a WinTV quadHDTV PCIe card from Hauppauge and the worst load I have is 4 recordings at a time where there may be some overlap caused by back to back recordings on the same channel where the recording rules have extended time at the end.
>>> 
>>> In the current backend I use ext4 on the boot SSD and the mirrors are set up as RAID 1 mirrors using mdadm. That works and I've been able to replace failed drives several times without a problem.  However, I've been researching ZFS and BTRFS and building test systems to play with both.  Since Ubuntu even allows 20.04 to be installed with ZFS, it looks promising. I really have no idea whether I should go down that path.
>>> 
>>> I figure that I could probably find a miniITX motherboard with a M.2 nvme boot socket and then since the WinTV card is low-profile, I could get a smaller chassis that only holds 2 drives.
>>> 
>>> Any thoughts would be appreciated.
>> 
>>  I'll add some thoughts here.  For background, I'm running with a mirrored set of nvme for boot + other storage (home directory, other bits), and a mirrored set 2 TB HD for recordings and other storage needs that need space but not performance.  I'm using ZFS for all of this.
>> 
>> Mythtv workloads are pretty kind on hard drives - it sends to be sequential reads and writes, which HDD are pretty good with. Sequential read/write speeds for HDDs tends to be pretty fast (I presume you are talking ironwolf HDD here - there are apparently also ironwolf SSDs).  Based on the specs, there should be more than sufficient performance for recordings & playback.
>> 
>> There is the suggestion that if doing mirrors or raids, you ideally want to mix different drive models/vendors.  The rationale is that if you are doing a simple mirror and running on 2 hard drives made at the same factory at the same time, these 2 drives are doing near the exact same workload. When one fails, the other will probably fail fairly soon - if you are on top of things, you can get that replacement installed before the second one fails.
>> 
>> ZFS has lots of nice features, but with mythtv, you probably are not going to care about most of them.  It may not be worth the learning curve to set up/maintain that vs something you are familiar with.
>> 
>> As an aside (since this is not the case going forward), if you had 4 hard drives, you could either do a raid10 (drives are mirrored, then striped together, providing redundancy and performance, and not needing to have 2 storage directories), or raid5/raidz, where you get the capacity of 3 hard drives + 4th for redundancy, but performance on this is worse (they probably still fine for mythtv).
>> 
>> I would think whatever you do, you want mirrored boot drives - otherwise if the boot drive fails, you are not recording/playing anything back until you get it replaced, re-install the OS, reconfigure everything, etc.  It wasn't clear to be if the miniITX option would have 2 NVME slots or not.
> 
> 
> Thanks for you thoughts.  As to mirrored SSDs, nvme or SATA, I've heard that RAID writes even in the unused spaces and reduces the life of an an SSD. What have you heard?

Jim myth here:
SSD life is now so bad per cell (1000 or 10000 writes) ssd manufactures quote life in TBW.
The TBW spec depends directly on ssd size.
After 1/2 a year in use the projected life of my m2 is 40 years (regrettably more than mine :-)

Model Number:                       Samsung SSD 970 EVO Plus 2TB
Power On Hours:                     3,741
Data Units Written:                 29,494,374 [15.1 TB]

This is a cheap m2 (4 cell) at 600 TBW, you can get more expensive 1200 even 2400 TBW ssds.

James
> 
> At present, my Production MythTV/NAS boot SSD is 2.5 SATA and I have a Conezilla image of it and it's only 16GB so I can use the cheapest available size.
> 
> I'm built a test system yesterday with 2 identical WD Hard Drives and a Boot SSD using Ubuntu 20.04.3 and used ZFS. The install for the OS is standard and to create the zpool for the mirrored HDs was one simple command. It even mounts the mirror for you after creation.  One change is the zpool is mounted on /NAS in my case and I would have to setup mythtv directory structure to use that. I'm going to install Mythtv today and see how it performs.  I ran some FIO benchmarks and it's not bad performance compared to bard metal.
> 
> I've even debated getting a real NAS like Asustor AS1104T and just use a simple small PC with Gbe Ethernet and a PCIe slot for the tuner. But the AS1104T is something else to manage.

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