[mythtvnz] SSD Drives for video

[Nick Rout]

On Sun, Jun 8, 2014 at 4:34 PM, Worik Stanton <worik.stanton at gmail.com> wrote:
> On the subject of using an SSD for recording onto...
>
> On 05/06/14 19:28, Pieter De Wit wrote:
>> Personally, I would avoid this as the ssd will wear out
>
> I expect that Pieter is thinking of memory wear
> (https://en.wikipedia.org/wiki/Flash_memory#Memory_wear).
>
> I am using my 30G SSD drive while my net-storage device is in the shop
> getting fixed.  I do not believe I am in danger of encountering problems
> with my SSD in this period.  But have been thinking that I will not be
> buying mechanical discs again.   Pieter's comments are food for thought
> and it is worth examining the issues.
>
> http://www.snia.org/sites/default/files/SSSI_NAND_Reliability_White_Paper_0.pdf
> says:
>
> "Another peculiarity of NAND Flash as a storage medium is its increasing
> susceptibility to bit errors after having gone through a certain number
> of program-erase (P/E) cycles.The number of cycles varies, depending on
> density (storage capacity per physical area), vendor, and NAND Flash
> type. Generally speaking, SLC is usually rated for ~100,000 P/E cycles,
> whereas MLC Flash is usually rated for ~5,000-10,000 P/E cycles. NAND
> Flash also becomes less reliable over time when unpowered."
>
> SLC is the older variety and MLC the newer variety, AFAICT.  Odd that
> newer varieties should be less durable.
>
> But for our purposes, recording video, surely even 5 to 10 K cycles
> would be OK?
>
> Cost is clearly an issue, with TB hard discs being so cheap c/f SSD, but
>  what are people's thoughts on using SSDs in Myth?  Is it worth the
> extra cost?  Is it worse than spinning discs (due to the limited P/E
> cycle)?
>
> What are people's experiences?

I have no experience of them, but the perceived wisdom of what I have
gleaned from the mythtv-users list is that they are worthwhile for
doing initial recording IF you have high volume multiple stream
recording requirements, eg you want to record 10 streams on a fairly
continuous basis (and also perhaps if you are doing a lot of live tv,
where you not only have to write but also read).

But most people that I have seen with that type of setup transfer the
recording to a spinning platter pretty soon after recording. For
example you can set your storage groups up so that all recordings
initially go to disks 1 and 2 (which will be ssd) but clients will
look on disks 1,2,3,4 and 5 for recordings, so the move from disk 1
(SSD) to disk 3 (normal disk) will be transparent to the end user.
(Not sure what happens if you move something while someone is actually
watching it!) Disks 3-5 may of course be in the same machine, or on a
NAS.