(SOLVED) Porting SSD from array to cache

[costianuv]

I've seen some other forum topic with a similar title but I don't think it applies to my case. First of I'm very new to UnRaid so please be gentle :D

After I've partly built my system I was keen on trying UnRaid and at the time I only had an SSD available(for which I had planned to use as a cache drive) so I've started the array like that and quickly found myself bathing in dockers(succesfully ported HA from my RPI3).

Now that my HDDs have arrived I want to safely move all of the data(appdata,system,etc.) from the SSD to one of them so I can repurpose the SSD as cache.

How should I go about this?

[testdasi]

Appdata, system should be on cache (SSD) and shouldn't be on a HDD due to the slower speed.

 

Do you just want to move the SSD from disk1 slot to cache slot?

If so, what's the file system of your SSD? xfs or btrfs?

 

If you just want to move the SSD from disk1 slot to cache slot, you don't need to move data in and out of it but I need to know what file system it is using to give you the necessary things to look out for (i.e. the silly new user mistake).

[costianuv]

Hey thanks for the quick reply!

1 minute ago, testdasi said:

Appdata, system should be on cache (SSD) and shouldn't be on a HDD due to the slower speed.

Yes that is also part of the endgoal.

1 minute ago, testdasi said:

Do you just want to move the SSD from disk1 slot to cache slot?

If so, what's the file system of your SSD? xfs or btrfs?

That's exactly what I want. SSD is using default xfs.

3 minutes ago, testdasi said:

If you just want to move the SSD from disk1 slot to cache slot, you don't need to move data in and out of it but I need to know what file system it is using to give you the necessary things to look out for (i.e. the silly new user mistake).

I'd appreciate that very much ❤️

[testdasi]

WIth xfs, the first and foremost thing to note is you cannot have a multi-drive cache pool.

That means in the future, you can replace the SSD with another but you can't add more drives to the cache pool (without having to reformat the pool to btrfs).

That is not necessarily a bad thing because:

• There are currently performance issue with multi-drive (btrfs) cache pool with some SSDs.
  • Strangely I have never had that issue but surely some users have had issue with it. You can do a quick search on the forum for more details.
• Unless you NEED mirror protection (i.e. RAID-1), it is generally better to have 1 SSD in the cache pool and 1 unassigned to separate read-heavy and write-heavy data. That will improve the lifespan of both SSDs.
  • I would also prioritise having a backup over having mirror protection.

 

 

With that out of the way, to move the SSD from disk1 to cache:

• Back up any data that is critical. Since you were just testing things out I assume there's nothing too important but worth a point to check it.
• Go to Tools -> New Config -> tick the box to confim your understanding and ok -> Main -> all slots should be empty -> MAKE SURE THE NUMBER OF DRIVES IN CACHE IS ONE -> Make sure there is only ONE slot for cache -> Select the SSD in cache slot + select HDD in the various array slots.
• Before clicking Start, MAKE SURE THE CACHE SLOT IS NOT BEING FORMATTED. It should be obvious on the GUI which drive is going to be formatted. If you already set it correctly to have a single drive cache pool (i.e. there is only a single slot possible for cache) then you should be fine here but it is always a good idea to double check..

If you are not sure, just take a screenshot and post and people should be able to help.

 

 

 

With regards to your HDD, make sure to run a preclear cycle on each of them (install preclear plugin from the App store).

It will take a while to complete but it's worth it.

Only reconfigure your cache and array AFTER preclear is all clear.

[costianuv]

Hi again,

Thank you for the very detailed reply!

I don't have any plan to set up redundancy for the cache (for now at least).

I will be backing up my HA as I was so pleased by the performance after I've ported it to UnRaid docker that I went all out and completely removed my RPi(questionable)

 

Currently in process of building the parity drive and pre clearing my other drives. Secondary question here:

Not sure if I should go through with the process of building the parity. Will it get invalidated by a New Config and have to start all over again?

 

LE: Marking as solved. Thanks for the support! Parity was indeed invalidated by a new config but nothing a few hours could not rebuild.

Edited May 7, 2020 by costianuv