RAID 0 cache drive


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I had looked over some different threads (listed below) that discuss how the cache pool is currently implemented in unRAID and its current limitations. Those being that btrfs RAID-0 can be setup for the cache pool, but those settings are not saved and "revert" back to the default RAID-1 after a restart. I also found a much older topic related to pre 6.0 that states that you can setup a BIOS RAID-0, however "unRAID will not be able to spin it down, or get the disk temperatures..." With that in mind, I really have 0 concerns about having parity or redundancy on my cache drives as I regularly backup my VMs and mover pushes over any cached data to the main array nightly. So, I would like to have my SSDs setup with RAID-0 (btrfs or BIOS) if possible, but have a few different questions in regards to this.


Is everything above still the current situation regarding RAID arrays as cache drives in unRAID?


Does anyone have a BIOS RAID-0 array set as their unRAID cache drive currently, and if so do you have any issues with it?


I know JonP made mention of not seeing the efficacy of having btrfs RAID-0 over "single", but I don't know enough about how that's implemented to be able to say I want one over the other. Has LT made any new comments as to when the btrfs RAID-0 option will be added (if it will be added)? Will we only be seeing "single"? What are the pro's and con's of "single" vs. 0?




Adding a second SSD under /mnt/cache WITHOUT RAID1  (Read 449 times)


btrfs cache pool  (Read 11135 times)


BTRFS vs. ZFS comparison  (Read 12147 times)


Topic: Combine disk in an RAID-0 cache disk.  (Read 4510 times)

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Thank you very much, this was pretty much exactly what I was looking for! I did do a bit more google'n and also found some articles expanding on my other questions related to why it would be better for most to switch from HW RAID to a software driven RAID solution. Since from your post it looks like making changes are no longer reverted upon a reboot in unRAID, I think I'll be going the btrfs RAID-0 route. Thanks again.

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Since from your post it looks like making changes are no longer reverted upon a reboot in unRAID, I think I'll be going the btrfs RAID-0 route. Thanks again.

AFAIK an established pool has NEVER been automatically reverted on reboot, but if you make changes to the pool you will have to manually adjust the balance command to reflect what you want, as the balance command defaults back to RAID-1. That may be what you are referring to, and that hasn't changed.
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Thank you for clarifying jonathanm! I reread the quote from limetech (below) a few times and think I see where my misunderstanding was. I think I was combining the two separate sentences and reading it as "sure you can try it out, but after a reboot it will change back to the default of RAID-1 AND auto rebalance." Seems like what it's actually saying is that only the 'Balance section options' will change back to default, so as long as you don't click balance again OR add another pool device, your RAID settings will remain as you had set them. Sorry so much time on this, but thank you both again for helping me to get a clearer understanding of it and also find my mistake!  :)


You can set up a raid-0 cache pool.  When you click on the 'cache' device after array Started and cache is mounted, scroll down to 'Balance' section and you will see default Balance options are:

-dconvert=raid1 -mconvert=raid1

You can change the 'raid level' by editing these options and click Balance.  For example, to have data raid0 but leave metadata raid1 you could change to:

-dconvert=raid0 -mconvert=raid1

You can monitor syslog to watch balance operation proceed.


Note that, at present, the s/w will "revert" the default balance options back to:

-dconvert=raid1 -mconvert=raid1

That is, we don't store your selection.  Similarly if you add a device to an existing pool it will automatically kick off a balance with the default options.  We plan to address this in a future release, but for now you can experiment with it.


EDIT: Following the instructions in the link posted, I now have my 2SSDs setup in a btrfs RAID-0. I did have to balance it a few times as RAID0 for it to finally update the Data section correctly (as was also noted in the other thread), but finally got it going correctly. The performance improvement is NOTICEABLE. Incredibly happy with this setup, thank you very much!

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  • 3 years later...

Hey, I've been running 2x SSD's in raid0 for quite a while now, and I'm getting some write errors on one of the drives as they're getting pretty old. I've got a single 1 tb ssd replacement (getting the second one later). 

So, how do I go about changing my cache to not use raid any more ? Should I just change the mode to "single" or will this delete the existing data? I'll do a backup first of course. 


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