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TODDLT

SSDs' and Dynamix Trim Plugin

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I have 4 SSD's in my unRAID server.

All for are Samsung 850 EVO's   

2 EA.  250GB for cache drives which are only used for dockers, mostly Plex

2 EA. 500GB for music and misc personal files (other than media), inside the array.

 

I know Plex does not technically support SSD's for the array but have exchanged on a couple different threads with johnnie.black and it sounds like from the testing he had done the 850 EVO's were pretty safe.  What I also THINK I recall from those exchanges is that the 850's did not need an outside trim command to stay efficient.

 

I recently installed "fix common problems" for the first time and one item flagged is that I am not using the Dynamix Trim plugin for my cache SSD's (along with warnings about my other two in the array).  As I understand it, the trim command is what causes much of the concern about using SSD's in the array, the parity would not update with changes made by trim.  

 

So my question at the end of this is should I be using Dynamix Trim?  on the Cache drives?  Does it even work on the drives in the array and should I be using it there too? or do I have the option for one and not the other?

 

I'll add to this, my cache drives house the Plex database.  Sometimes, and only at a random occurrence, the local Plex client hangs when opening a specific movie, show, album.  the first times it would just hang for 3-5 seconds but now it's hung for 10-20, not every time and not at any other point but actually opening the selected media.  Navigating within the collection is speedy and without incident.  I have no way to know if this is related to drive speed because the cache drives need to be trimmed or not, but I thought I'd ask about it before jumping ahead.

 

Thanks in advance.

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3 minutes ago, TODDLT said:

So my question at the end of this is should I be using Dynamix Trim?  on the Cache drives?  Does it even work on the drives in the array and should I be using it there too? or do I have the option for one and not the other?

Yes, you should be running the trim command on the cache drive.  My understanding is that issuing the trim command against a drive in the array *may* cause parity to be out of sync ( @johnnie.black? )

 

If it does, then you want to ignore the error from FCP, and manually run the trim command daily / weekly / monthly against the cache drive alone

fstrim -v /mnt/cache

using the user scripts plugin

 

If there's no issue with doing the trim command against array devices, then install the SSD trim plugin as it does every SSD found on the system.

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1 hour ago, Squid said:

Yes, you should be running the trim command on the cache drive.  My understanding is that issuing the trim command against a drive in the array *may* cause parity to be out of sync ( @johnnie.black? )

 

If it does, then you want to ignore the error from FCP, and manually run the trim command daily / weekly / monthly against the cache drive alone

 


fstrim -v /mnt/cache

using the user scripts plugin

 

If there's no issue with doing the trim command against array devices, then install the SSD trim plugin as it does every SSD found on the system.

OK well, I'll set up trim on the cache as you suggested and wait for johnnie.black on the other drives.

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It depends on how much free space the drive has, and how much writes the drive gets - because the trim is used to prepare released disk space for quick reuse. So it really matters a lot what usage patterns the drive sees, i.e. how fast it will consume the full pool of free flash blocks and will then have to slow down while doing just-in-time block copy/erase instead of having free blocks pre-cleared.

 

Note that trim isn't just limited to pre-clearing flash blocks - it's also about letting the drive know the amount of in-use information on each flash block so it knows what existing data on a flash block that needs to be moved to a different block to free the previous block for erase.

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