Need some input on replacing/adding a second cache drive

[Laucien]

Hi!

 

I have a 750GB SSD as cache drive in my unRAID server. Currently it is storing the usual cache stuff along with a bunch of docker images and in the near future will have a couple extra VMs and software (planning to make the server double as a gaming vm). 

 

I want to get a second SSD but I'm not sure if I should get another 750GB or go for 2x1TB drives and use the 750 solely for the gaming VM and Steam library. 

The main problem I have with adding another 750GB drive is that the only one I can find on Amazon.com is the same one I have which costs almost as much as the 1TB version (I bought it on sale last year for like US$100). 

 

So a couple questions. If I get the 1TB and pair it with my current 750GB I know I'll only have 750GB of usuable cache but can I use the extra storage for something else (like unassigned drive) or that's not possible?. 

If I decide to buy 2 1TB SSDs, which ones would you guys recommend? I'm looking for something along this price range.

 

Thanks!. 

[danioj]

There is no reason why you cannot have all the space available to you if you buy a 1TB SSD.

 

If you format the SSD's as BTRFS you can run them in RAID0 and unRAID will treat them as 1 big drive.

 

I run 3 x 250GB SSD's and unRAID see's them as 1 big 750GB cache disk. I don't run anything outside the array (utilising unassigned devices plugin) anymore as I prefer to use unRAID as it was intended (VM's, Docker etc) from the Cache device.

 

As for the type of SSD, I don't think you can go past the Samsung EVO range. I find them to be excellent value for money.

[JorgeB]

Raid0 won't use all space from two different size devices, but you can use the single profile.

[Laucien]

7 hours ago, danioj said:

There is no reason why you cannot have all the space available to you if you buy a 1TB SSD.

 

If you format the SSD's as BTRFS you can run them in RAID0 and unRAID will treat them as 1 big drive.

 

I run 3 x 250GB SSD's and unRAID see's them as 1 big 750GB cache disk. I don't run anything outside the array (utilising unassigned devices plugin) anymore as I prefer to use unRAID as it was intended (VM's, Docker etc) from the Cache device.

 

As for the type of SSD, I don't think you can go past the Samsung EVO range. I find them to be excellent value for money.

 

Wait, but I thought forming a cache pool with 2 drives in unRAID would treat them as the equivalent of a RAID1 with both disks being mirrors of each other. That's why I assumed that if I pair a 750GB SSD with a 1TB one I would end up with 750GBs of 'mirrored' storage with the other 250GB going to waste. 

 

Am I getting that wrong?. 

 

6 hours ago, johnnie.black said:

Raid0 won't use all space from two different size devices, but you can use the single profile.

 

Sorry, I don't think I got what you meant by that. 

Edited April 5, 2017 by Laucien

[JorgeB]

1 minute ago, Laucien said:

Sorry, I don't think I got what you meant by that. 

 

By default a cache pool will be raid1 mirror, and with 750 + 1TB you'd only have 750GB usable.

 

Like danioj posted the profile can be changed, if you change to raid0 and with the same devices you'll only have 1.5TB usable, single profile is the only one that can use all the space from 2 different size devices, obviously without redundancy or any performance advantage.

 

See here for more info on the available profiles:

 

[trurl]

Lots about this in the V6 FAQ. Scroll down to Cache Drive/Pool section

 

[Laucien]

I didn't know that was possible. Just thought the only option for cache drives was going with RAID1. 

 

Thanks for the links and help :D. 

[Laucien]

OK, this is a complete departure from what I mentioned on my first post but still falls on the same subject jaja. 

 

On my desktop I have a MX100 512GB SSD from Crucial, I'm going to buy an MX300 525GB SSD also from Crucial and I'll put them both into a cache pool in my unRAID server. Just to be 100% sure. In the default RAID1 mode it uses I will have redundancy but I will only be able to use 512GB limited by the smaller SSD, right?. The drives not being exactly the same shouldn't matter either, right?.

 

Really, as much as I'd love to have 1TB of mirrored SSD storage for cache it's totally overkill for my needs and I'll have better use of half that cache (still mirrored) and take the 750GB SSD to use as steam library in my main rig haha. 

Edited April 11, 2017 by Laucien

[trurl]

22 minutes ago, Laucien said:

On my desktop I have a MX100 512GB SSD from Crucial, I'm going to buy an MX300 525GB SSD also from Crucial and I'll put them both into a cache pool in my unRAID server. Just to be 100% sure. In the default RAID1 mode it uses I will have redundancy but I will only be able to use 512GB limited by the smaller SSD, right?. The drives not being exactly the same shouldn't matter either, right?.

Right.

Right.