Best SSD for cache disk?


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I'm using a 1TB Samsung 850 EVO.

 

My personal opinion is the 850 PRO is not necessary for a vast majority of users.

And for cache disk, even the 850 EVO is unnecessary - pretty much any branded SSD will do.

 

The only reason I use the EVO for my server is because I have 1 lying around (and that my much older Kingston 128GB SSD is not big enough).

 

 

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I'd recommend an mlc drive over a tlc. Most tlc drives have horrible write speeds. But don't pay attention to the advertised write speed because they cheat.

 

What they do is they put a couple gigs of slc (really fast) and the rest of the drive is tlc. So the first 2GB of data will write at the advertised speed but anything above that will write at the tlc speed which can be slower than some spinning drives (common ssd speed tests out there use small files for the tests and don't saturate the cache so what you're seeing advertised is the slc cache speed. Imagine if unraid advertised the cache drive write speed instead of the array write speed, people would be outraged). They are more like those seagate hybrid drives where a spinning drive has a flash cache, but in this case a slow ssd has a cache of fast ssd. Check the reviews for "sustained write" speeds and you'll see the speed drop. If you're copying large files to the cache drive (I do) then you'll experience the slow writes.

 

I believe the only tlc drive that is highly recommended is the samsung evo 850 and that's because it uses a different technology (3d nand) and has fast writes that rival mlc drives

 

Unfortunately most cheaper ssds out there are tlc with slc cache these days. Even some models that used to be mlc are switching to tlc (like the crucial bx series)

 

Anyway, I recently got myself a couple of 240gb zotac premium edition mlcs for $65 each, but they now seem to be out of stock (beware that the non premium version is tlc). They were highly rated and work really well in an unraid cache pool

 

PS. tlc is the type of flash memory that's typically used in usb flash drives. And it's much cheaper than mlc or slc

 

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3D NAND is basically TLC but stack vertically instead of horizontally. Apparently it results in faster speed and longer lifetime.

 

Also, IIRC, Samsung also has a "clever cache", for a lack of better word, which basically treats each TLC as a giant SLC so pretty much the entire free space is used as cache (so total cache = free space / 3 - some overhead). That's why Samsung software on PC allows over-provisioning, which basically reserves empty space readily useable for this "clever cache".

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  • 2 weeks later...

Sorry to butt in here and not start a new thread, but I'm also considering a cache drive for my new unRAID as a place to store my future Dockers (Plex, LMS, sickbeard, sabnzbd, transmission, maybe more) [note that I only have 2x drives (1x storage, 1x parity) in there at the moment, so speed isn't yet a problem].

I'm leaning toward a Samsung 750 EVO or Intel 535 (just on brand strength alone - I know nothing about the drive - any other recommendations are appreciated) but am unsure of what size is best - 240GB or 500GB.

 

It's unlikely I'll ever transfer close to even 100GB in a single day, but I'm concerned about how much space the Dockers will take up (and VMs, should I go down that path later).

How much space should I expect? I saw on the Plex forums that someone mentioned that Plex ate through their 120GB cache drive pretty quickly, and don't want that to happen to me. See: https://forums.plex.tv/discussion/comment/855869/#Comment_855869

 

Note that in a few months' time (perhaps as much as 6 or more), I will likely be replacing my desktop PC, so will have 2x 120GB SSDs available to add to the cache, too, but I will need to purchase a mounting bracket (US$50 after shipping http://homeservershow.com/hp-microserver-gen8-drive-bracket.html) and a PCI-E > SATA card to attach them to my server, so may never end up doing it.

 

Also note that my server is still being set up - I'm yet to install any apps/dockers/VMs on it at all (thus my confusion on how much space I should allocate to it).

Thanks all for your help.

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The 750 EVO, AFAIK, is a 2D TLC design (vs 3D TLC design of the 850 EVO). So you will end up with the same TLC slow down which aptalca mentioned. To be honest, it should be sufficient (with Dynamix Trim plugin) but keep that in mind.

 

I have 7 dockers including Plex and they only occupy 38GB (I set the image to 32GB size so app data only about 6GB). I reckon the issue with Plex is an anomaly.

240GB would be sufficient for average uses. 120GB might be a little too low but serviceable. 500GB is enough for most people.

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The 750 EVO, AFAIK, is a 2D TLC design (vs 3D TLC design of the 850 EVO). So you will end up with the same TLC slow down which aptalca mentioned. To be honest, it should be sufficient (with Dynamix Trim plugin) but keep that in mind.

 

I have 7 dockers including Plex and they only occupy 38GB (I set the image to 32GB size so app data only about 6GB). I reckon the issue with Plex is an anomaly.

240GB would be sufficient for average uses. 120GB might be a little too low but serviceable. 500GB is enough for most people.

 

Thanks so much for the info! I thought that 120GB seemed rather excessive for a Plex install...

Looking at the price difference between the 750 and the 850, and the fact that the 850 comes with a 5 year warranty, I reckon I'll go the 850 EVO.

Will take a look at my budget and decide if I can afford the extra £££ for the 500GB model or not and buy accordingly.

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Just wait until your Plex libraries grow a bit.  My Plex appdata is approaching 100GB.  And that after removing music.  With music it was over 130GB.

If you don't particularly care about it, turn off thumbnail generation.  My appdata is 19.5G with 18k TV Ep, 3k Movies
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Just wait until your Plex libraries grow a bit.  My Plex appdata is approaching 100GB.  And that after removing music.  With music it was over 130GB.

If you don't particularly care about it, turn off thumbnail generation.  My appdata is 19.5G with 18k TV Ep, 3k Movies

 

Thanks, but I have never had them enabled.

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Just wait until your Plex libraries grow a bit.  My Plex appdata is approaching 100GB.  And that after removing music.  With music it was over 130GB.

 

Holy hell. I was considering using Plex for music (for remote streaming; I use Logitech Media Server for music around the house), but I can't imagine the size of the library with ~35k songs.

Perhaps I shall opt for the 500GB cache drive, then.

 

If you don't particularly care about it, turn off thumbnail generation.  My appdata is 19.5G with 18k TV Ep, 3k Movies

 

Good tip. If this is a local cache of internet files, then I should be ok as I have a good, fast, reliable internet connection here.

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My plex folder is 110GB mainly because of the media index files (video preview thumbnails). For each media file, it creates a bif file that contains thumbnails taken every 30 sec or a minute (not sure about the actual frequency) but these files tend to be 10-30MB each. So if you have thousands of movies and tv shows, they take up a lot of storage space.

 

They provide nice thumbs while seeking/fast forwarding like netflix does.

 

You can turn that feature off if you like and you don't have to worry about it. Plex will only take a few gigs total.

 

Or, you can move the folder containing those files to another location and add a symlink.

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  • 2 weeks later...

Currently I have been running OCZ Vertex 4 (256GB) with no issue so far since two years.

I had also Samsung 830 Pro and Crucial MX100 as an cache drive without any issue.

Last year I tried OCZ Vector 180 and had some issue with the file transfers and I/O operations as the system hangs for few seconds.  I read somewhere that this is the issue with controller on that particular ssd.

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What they do is they put a couple gigs of slc (really fast) and the rest of the drive is tlc. So the first 2GB of data will write at the advertised speed but anything above that will write at the tlc speed which can be slower than some spinning drives (common ssd speed tests out there use small files for the tests and don't saturate the cache so what you're seeing advertised is the slc cache speed. Imagine if unraid advertised the cache drive write speed instead of the array write speed, people would be outraged). They are more like those seagate hybrid drives where a spinning drive has a flash cache, but in this case a slow ssd has a cache of fast ssd. Check the reviews for "sustained write" speeds and you'll see the speed drop. If you're copying large files to the cache drive (I do) then you'll experience the slow writes.

 

Ah I didn't realise that. I hate when manufacturers basically lie.....they should get into politics!!

I bought a SanDisk X400 512GB  because i saw    Read 540MB/s, Write 520MB/s, 93.5k IOPS 

I was happy with it, but know i know about how they test I dont like it now!!!!

.......damn maybe ignorance is bliss !!!!  Thanks aptalca now im disappointed with my server again lol ! :)

 

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