Old SSD for TV Cache? (1 Viewer)

[Der_Bub]

Hello,

currently I use a RAM Drive for TV Cache. Now I have an "old" SSD for which I have no use anylonger (and on eBay it does not much), so would there be any disadvantages from using the SSD instead of the RAM drive (especially Channel switching times)?

Or can I use it to have longer times to rewind a show?

Thanks!

 

[mm1352000]

Hello

so would there be any disadvantages from using the SSD instead of the RAM drive (especially Channel switching times)?

Well, in terms of I/O speed, SSDs have higher latency and lower bandwidth than RAM. In short: they're slower. Therefore you would expect that channel switching times and seeking (rewind, fast-forward, seek/step) would be slower with an SSD... but I can't tell you how much slower. You would have to test that yourself. The difference could be insignificant/unnoticeable.

Or can I use it to have longer times to rewind a show?

"Rewind time" depends on the size of the time-shift buffer. Assuming that your SSD is larger than your RAM drive, you should be able to have a larger time-shift buffer. Therefore, yes, you should be able to use it to have longer "rewind time".

 

[CyberSimian]

so would there be any disadvantages from using the SSD instead of the RAM drive

An interesting question. Some points:

(1) At www.TheGreenButton.tv, there was a WMC user who decided to use a USB memory stick as his live-TV buffer. He tried at least two memory sticks, but each one lasted only a month or two before it started to develop errors. He decided that a USB memory stick was a bad choice for the live TV buffer.

(2) At forums.lenovo.com, there has been some discussion recently about the relatively poor performance of M.2 PCI-Express SSDs when installed in laptops; see page 2 of this thread:

https://forums.lenovo.com/t5/Lenovo...-Windows-7-amp-Windows-10/td-p/3427918/page/2

Apparently, SSDs can produce a lot of heat, and in the confines of a laptop case with its poor cooling, thermal throttling can significantly reduce the speed of the SSD, if the SSD has the appropriate firmware installed.

(3) I conclude from this that SSDs and USB memory sticks can suffer significant reduction in useful life if they are allowed to overheat for extended periods of time. Laptops avoid this by using SSD firmware that limits performance. If the SSD that you are thinking of using does not have such firmware, you might need to take extra steps to ensure that it does not overheat (such as a heatsink, or an additonal fan, or both).

In normal operation, Windows is constantly reading from and writing to the OS disk, but I suspect that the "duty cycle" is still quite low. When you use an SSD for live TV, the duty cycle must be approaching 100%, so there is no time for the SSD to shed the heat produced, and hence there is a risk of the SSD overheating.

(4) I will be building a new HTPC soon, with an SSD for the OS disk; but the live TV buffer will be placed on a RAM disk!

-- from CyberSimian in the UK

 

[RonD]

I will be building a new HTPC soon, with an SSD for the OS disk; but the live TV buffer will be placed on a RAM disk!

I agree with this comment, SSD are good for OS system disk applications that need high speed writes but don't to non-stop heavy write activity like a HTCP/DVR time-shift buffer.

The key limitation for SSD, Flash thumb drives is Write Endurance the number of times you can erase and write each individual bit in the Flash Memory. SSD designed for main OS system disk applications provide Write Leveling or Wear Leveling where the SSD internal disk controller logic detects heavy write traffic to some disk locations and does remapping of the writes to other locations to spread out writes over many disk blocks.

Typically there are limits to the number of writes you can do to a SSD, for example the Samsung EVO-850 drives are spec'd to support 75 Terabytes (75*1000 GB). If you do 10 GB/hour of time-shifting you would hit the limit in about 7500 hours, so, SSD lifetime would depend on the number of hours/year you use the HTPC. Other SSDs have different limits, and USB-Flash/Thumb drives typically don't spec the number of writes you can do before the drive wears out.

The memory bits stored in SSDs, USB-Flash/Thumb use special Floating Gate Transistors to save the data bits. For read operations the internal voltages are 1 to 2 volts. For Writes and Erase of data bits the flash memory uses 10 to 20 volt internal signals to clear or write the data bits. When a large number of writes are done to the same transistor it causes wear-out "technical difficulties" and problems trying to read, write, and erase data.

If you want more info, google any of the bold terms, the Oracle of Google has an infinite number of pages of information on SSDs and Flash drives.

 

[Skywizard]

I was using a USB stick for the time shift buffer on my Win7 Media centre quite successfully - occasionally it would have a hissy fit and a format of the stick would restore functionality.

I tried the same with the same PC and mediaportal and Win 10. I got what I thought were reputable, fast USB 3 sticks. The first one did not last long before it failed - I was able to get it replaced under warranty, The second one went the same way and it again failed and replaced under warranty, so I gave up. I could have tried a different brand I suppose. I like the concept of using a USB stick, they are easier and cheaper to to replace if they last a reasonable time.

 

[RonD]

My guess is reformatting gave windows a chance to detect/remap bad blocks to avoid using warn-out parts of the thumb drive. The thumb drive's internal flash controller also has logic that tries to detect/remap bad blocks. From a personal point of view, I view Thumb drives as a "2016 floppy drive" with N*GB data storage. Good for moving data around, but not really a high performance "disk drive".

At one time I experimented using thumb drives for time shifting with 2 or 3 thumb drives I had on my desk. One worked ok for the 1 afternoon of testing I did. The other 2 did not work well. They would start ok but every few minutes there would be on-screen glitches with lots of dropped frames. Played with windows file explorer to watch the files in the time shift folder, and Resource Monitor (DIsk) to see what windows showed for disk activity.

The every few minutes "glitch" seemed to happen when TV Server switched to a new time shift file every 256-MB. Resource Monitor also showed a large spike in queue depth (number of rd/wr commands waiting for the drive). I guess when the tv server reach the end of each time shift file, windows and the thumb drive needed to fully flush/commit all write data to the drive, open/start writing the next time shift file and triggered lots of erase/write activity in the thumb drive that took extra time to complete. Went back to using an internal HDD for time shifting.

 

[nfox]

I have been using a 120GB SSD partitioned as 60GB for the OS and MePo, and 60GB for the time-shift buffer for almost 2 years without any issues. I would guess that the TV is time-shifting for at least 4 hours a day. I did some very basic arithmetic based on a standard definition time-shift buffer stream using 2GB per hour (this is a number I think I remember from posts on this forum and elsewhere, but please correct me if I am way out).

2GB per hour for 4 hours = 8GB per day
8GB per day for 7 days = 56GB per week
56GB per week for 52 weeks = 2,192GB per year

So, if you watch SD telly for four hours a day for a year, approximately 3TB of time-shift data will be written to the disk in that time.

I have had a very quick look at the specs of a couple of 120GB SSDs and one claims a total endurance of 30TB, and the other 60TB. Taking a worst case scenario of 30TB and dividing by 2 (it's a 60GB partition) gives an endurance of 15TB. Or 5 years of use. I reckon that's not bad, considering how cheap small SSDs are these days.

I suppose if you are time-shifting HD content for 12 hours a days, and/or I'm horribly wrong with my guesstimate of buffer bandwidth, then an endurance of 15GB is not much, but there are SSDs claiming double the endurance, and you can use a bigger SSD.

 

[Skywizard]

I have been using a 120GB SSD partitioned as 60GB for the OS and MePo, and 60GB for the time-shift buffer f.

Isn't 60 gig for time shift a bit much? With the settings I used to get 1 or 2 hours of time shifting I used around 12 or so gig so for me (when I was using) a 32gig USB stick was an overkill. I suppose it all comes down to how much time you need on the buffer?

 

[nfox]

You're right it's a lot of space, and it's more than I ever actually use. This is a dedicated HTPC with an SSD for the OS, MePo and plugins, and a few utilities, so it starts up, and resumes from S3 standby as quickly as possible. It also has a mechanical HDD for recordings and media files because I can't afford a 2GB SSD. This left a lot of unused space on the SSD so I thought I may as well use it for time-shifting, and as I said, the bigger the space to write the buffer, the longer the disk will last. The time-shift buffer itself isn't configured to be that large - about 60 minutes of HD content.

It's not necessary to create 2 partitions, of course. I did because I have always kept the time-shift buffer on a separate partition for some reason that I now can't recall (basically, it's become a tradition, or an old charter, or something).