Mailing List Archive

On Sun, Jun 8, 2014 at 4:34 PM, Worik Stanton <worik.stanton@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.

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> SLC is the older variety and MLC the newer variety, AFAICT. Odd that
> newer varieties should be less durable.
>
I haven't overly kept up to play with SSD changes in the past year but
did spend time investigating them for work a few years ago, we couldn't
get approval for the small RAMSAN device we would have liked (priced at
$50,000+) and there were many issues with all sorts of problems with
different brand SSDs and also problems with OS support, depending on
controllers used etc. In the end I decided to get a couple of
reasonable SAMSUNG consumer drives on the basis that they should last a
couple of years before needing replacement and by then prices would have
dropped further (in practise not as quick as I thought they would) and
speed further improved (which they have). The database usage was a
little unusual with mass amounts of random read/writes and mass amounts
of sequential IO (which stayed on hard drives) and being completely
unloaded and reloaded every few days.

SLC is much higher quality and MUCH more expensive, generally found in
enterprise drives. MLC is a cheaper alternative where they use a
variety of techniques (wear levelling, extra non visible space etc) to
try and get an acceptable lifetime out of a drive.

Intensive small random writes used to be lifetime killers as writing one
byte required a full block write and cheaper drives didn't have overly
long write lifetime expectancies.

If you can afford them SSD's are fantastic. For MythTv I now use one
for OS/database/development and all recordings are on hard disc drives.
My TV front end uses a SATA SSD DOM which isn't overly fast and may not
last long (I like my gear to last forever) as I haven't gotten around to
minimising logging but it's tiny, silent and was cheap on AliExpress.


Mark




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On Sun, 8 Jun 2014 17:16:20 +1200, you wrote:

>On Sun, Jun 8, 2014 at 4:34 PM, Worik Stanton <worik.stanton@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.

If you are recording 10 streams at once, then you can just have 5 hard
drives and that will solve that problem. If you are recording 10
streams at once, then you will likely need all the extra hard drives
to store all those recordings anyway, so it does not make so much
sense to store to SSD first and then copy to a drive you could have
written to directly.

I have 6 recording drives now, and I am recording 4 programmes
currently. I am fairly sure I have had times when I am recording 6 or
even 7 programmes at once, but even if they were all overlapped by new
recordings directly afterwards (14 streams at once), with 6 drives I
would not expect any problems. I also have 8 Gibytes of RAM which
helps too, as mythcommflag runs in real-time from the RAM buffers,
rather than doing disk accesses.

Where SSDs are good for MythTV is for the database. When the
scheduler runs, it uses a huge number of database accesses very
quickly, and an SSD can speed that up enormously. My scheduler times
are getting annoyingly long, so I am contemplating an SSD, but can not
afford one quite yet.

The latest and fastest SSDs use a PCIe bus connection, as they are now
too fast for the old SATA specifications. The latest SATA
specification update includes connecting drives that way.

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On Sun, Jun 8, 2014 at 4:34 PM, Worik Stanton <worik.stanton@gmail.com>
wrote:

> But for our purposes, recording video, surely even 5 to 10 K cycles
> would be OK?
>

Yes, it would be fine.

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)?
>

The only reason I can see for considering one is to make a combined FE/BE
silent. Whether that's worth the extra cost depends on your sensitivity to
noise from the drive.

I have a SSDs in my main desktop and the machine I use at work. I wouldn't
buy another desktop machine without one, but I'm not so convinced of the
value for a 24/7 server that has sufficient ram.

Cheers,
Steve

On 09/06/14 01:39, Steve Hodge wrote:
> I have a SSDs in my main desktop and the machine I use at work. I
> wouldn't buy another desktop machine without one, but I'm not so
> convinced of the value for a 24/7 server that has sufficient ram.
Agreed.

I've installed a 500GB hybrid drive in the missus' laptop, and its
definitely a good compromise, has all the size and much of the speed,
but still has noise and no battery saving.

New desktops and laptops should be SSD, servers can be either based on
cost/performance requirements.

--
Criggie

http://criggie.org.nz/


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Thank you every body. This was very helpful. Food for thought

Worik

--
The only true evil is turning people into things....
Granny Weatherwax
worik.stanton@gmail.com 021-1680650, (03) 4821804
Aotearoa (New Zealand)