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

[Simon]

Mark Wedel <mwedel at sonic.net> wrote:

> Mythtv workloads are pretty kind on hard drives - it sends to be sequential reads and writes, which HDD are pretty good with.

Reads, yes sequential (mostly)
Writes, definitely not. Each recording causes a minimum of 2 seeks/second - write a bit of data, seek, update the metadata, seek, write a bit more of the stream, … Especially with multiple recordings, that can be a lot of head movement - albeit not as hard work as (say) a well worked database without adequate caching.



> James Abernathy <jfabernathy at gmail.com> wrote:

> When you mirror your SSDs are you using mdadm Mirror or ZFS Mirror. I know how to set up a ZFS or mdadm mirrors for data drives but If I use an SSD, either SATA or nmve, to boot from the setup for a mirrored boot drive is a lot more complicated from the blogs I've seen. How do you do it? 

I “just do it” !

I think GRUB has dealt with this for a long time, but also as long as you keep to the legacy V1 metadata format for madam mirrored sets, each partition in the set will act (read only, for booting from) the same as the array itself. That’s because if you use the older format, the metadata is at the end of the partition and the actual data (filesystem) starts at the beginning of the partition. So you can boot from sda1, sdb1, or the array that they are part of - when I first used software raid, I don’t think GRUB did handle arrays for booting and “inertia” means that I still tend to use the V1 metadata format for my boot partition !



James Abernathy <jfabernathy at gmail.com> wrote:

> Based on 600 TBW, I could record all the programs in Primetime on the 4 Major networks in the USA everyday plus some assorted other stuff at an average rate of 5GB/hour and use up the SSD in 24.93 years.  So if I make it to 94, then I'll have to rebuild. :-)

Or it could fail next week - but it’s OK, they’ll send you a nice new but blank one to replace it.
Kingston have just sent me a new 240G drive to replace one that failed. In this case I could probably recover the data because it works for a while and then “just disappears” off the bus - not that I need to as it was half of a mirrored pair.
Now, if it’s a standalone drive, with years of recordings on it - a replacement for the failed drive isn’t much compensation for it’s failure :-(


Simon