To Cache drive or not to Cache drive?


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Because the MLC wasn't working.

 

Not that it matters because neither works properly.

You must be joking.

The only thing that couldn't work is the controller. The type of memory doesn't matter in this case.

What matters is that TLC memory is worst choice for UNRAID, because this system doesn't have trim support.

 

This is incorrect. The  Samsung Evo SSD is a TLC device with TRIM support. TRIM is implemented in the controller. The 840 EVO’s MEX controller supports SATA 3.1 TRIM commands. TCL vs MLC refers to the bit density and has nothing to do with the controller, SATA, or TRIM.

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I'm curious if this is possible.  I have 20 drive array consisting of mixed 4tb and 2tb drives.  All drives are currently used for storage.  I just swapped out a couple of my older 2tbs for a new 4tb reds.  For the first time in awhile I'm space rich (5.3tb of free space).

 

Due to extra space I'm wondering if I can transfer my data out of one of my existing 2tb data drives (2tb hitachi 7200rpm) and use it as a tepid spare/cache.

 

I guess it's more curiosity if I could reassign a data drive to a cache and then possibly back to a data without issue? And if there's any potential risks trying this out.

 

I'm not currently dissatisfied with performance and data was more the priority over performance previously.  But since I have the opportunity now to give this a try I'm a little curious. 

 

Thanks any feedback would be greatly appreciated. 

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  • 1 year later...

DANG!  I just saw this:

Edit: (8/13/2012) It has come to my attention that the Intel Atom CPUs are slow enough to cripple write performance when using modern SSDs as a cache drive! If your goal is a low power yet high performance server, then you will be best served by an i3 CPU (or better) as opposed to an Atom. For more info and a detailed account of the Atom's limitations, see jowi's plight later in this thread. The discussion spans four pages, so to skip right to the hard evidence of the Atom maxing out and limiting write speeds, click here. Evidence of fast, non-crippled SSD write speeds can be found here.

 

After wondering why the brand new 850 Pro on my X7SPA-HF-D525 is only obtaining 40-50 MB/s writes... no faster than the 5400 RPM drive I replaced

....

I am hitting other limitations with the Atom too (not beefy enough for the Dynamix File Integrity plugin for example)

....

May be time for a full blown ECC upgrade :)

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There have been several examples of how much more CPU-intensive v6 is.    And in addition to its higher NAS-only CPU usage, there are clearly significant CPU resource requirements for Dockers, VM's, etc. ==> in short, if you're building a new UnRAID system you do NOT want to skimp on CPU "horsepower".

 

Personally, I wouldn't recommend using anything that scores less than 5,000 on PassMark ... and if I was building a system myself I'd use a CPU that scores over 10,000.

 

 

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I FULLY agree Gary.  It is still a good NAS ONLY system... but struggles now even when doing a single preclear+parity check+single stream.

 

I doubt you'd have any issue doing a pre-clear and a stream; but doing a stream during a parity check is likely to cause issues on a lot of systems ... especially if they have a relatively low amount of memory.

 

My D525-based server works just fine as a NAS ... it's primarily used to backup all of my computers; store all my program CDs/DVDs (nearly 2 decades worth);  and backs up the TV recordings on my primary HTPC.    Except for an occasional stream of one of the TV shows, it's not used for media streaming ... and certainly is never used for that during a parity check.    But I've had no performance issues with it at all ... it's got 6 3TB WD Reds (no cache) and has been absolutely rock solid ever since I built it => until a very recent power failure when the UPS shut it down, it had over a year of uptime (last boot before the power failure was when I updated it to 5.0.6).

 

I also didn't upgrade that particular server to v6, due to the performance issues I've seen on relatively low-power systems with that upgrade.    My media server was upgraded, and it works just fine with a Pentium E6300 (PassMark 1706) ... but that's well above the 700 PassMark of a D525.    It has no problem supporting 4-5 simultaneous streams (haven't tried more than that) ... although, again, I never stream during a parity check.

 

 

 

 

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I am running a Intel Xeon E3-1230 @ 3.20GHz .. It gets a score of 7899 and it extremely fast.. I have yet to see its cpu peeking above 40%... And I am running a VM and 5 ot 6 dockers..

 

Not surprised at all ... an E3-1230 is a very good CPU => although not quite 10,000, it still has a very respectable PassMark ... well above the 5,000 I noted above.

 

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Posted elsewhere but maybe this is a better place. I have a single M.2 Turbo drive, in addition to 4x 250GB SSDs, how is it best to utilise the M.2 drive, bearing in mind I want to use VM's and Dockers.

What version of unRAID are you running? This is a v5 forum.

 

If on v6, can you see that drive in Unassigned Devices?

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Posted elsewhere but maybe this is a better place. I have a single M.2 Turbo drive, in addition to 4x 250GB SSDs, how is it best to utilise the M.2 drive, bearing in mind I want to use VM's and Dockers.

What version of unRAID are you running? This is a v5 forum.

 

If on v6, can you see that drive in Unassigned Devices?

 

what an idiot, sorry. yes I'm on version 6. yes I can see it in unassigned devices.

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  • 4 weeks later...

I just allocated a cache drive to my unraid 6 machine. It's a 10,000rpm raptor drive. Now, from my understanding everything I put on the server is meant to go on the cache drive and then after a certain time it's written to the other drives. When I add files now, say 20gb worth, I'm not seeing the data change on the cache drive. It's always 17mb. Am I missing something?

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I just allocated a cache drive to my unraid 6 machine. It's a 10,000rpm raptor drive. Now, from my understanding everything I put on the server is meant to go on the cache drive and then after a certain time it's written to the other drives. When I add files now, say 20gb worth, I'm not seeing the data change on the cache drive. It's always 17mb. Am I missing something?

The cache drive only caches user shares that have been configured to use the cache drive. Each user share has settings and you must set each user share you want to cache writes to Use cache: Yes.

 

To clarify some other points about your understanding. Writes to disk shares are never cached, only writes to user shares. And cached files aren't written to the other drives after a certain time, they are written to the user shares at a scheduled time. The user shares are of course on disks but as mentioned each user share has its own configuration.

 

If you create a user share, unRAID will create a top level folder named the same as the share on one or more disks as needed and depending on that user share's settings.

 

Conversely, any top level folder on cache or any array data disks is automatically a user share named the same as the folder. If you don't configure a user share it will have default settings.

 

See the wiki for more about user shares. There is also a help button in the webUI that you can turn on or off that will explain things, and there is pretty extensive help for the user share settings page.

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  • 2 years later...
11 minutes ago, Stan464 said:

Writing on an Old Topic but what happens if you use a 120GB SSD as Cache but you Over Util. Would it spill over and hit the array directly? or simply corrupt and state No Space or something?

 

Thanks kindly.

 

Depends on the use cache setting (and an appropriate setting for minimum free space)

 

https://lime-technology.com/forums/topic/46802-faq-for-unraid-v6/?do=findComment&comment=537383

 

 

Edited by johnnie.black
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