Multiple drive cache questions

[Madoc]

Google seems unable to answer my specific questions, but it might be more that I dont know the terms to search for/what I'm reading.

Drives:

1X 256g lighton SSD

1X 250g 840 EVO

1x 500g 860 EVO (brand new)

As an additional wrinkle, this mboard only has 2 sata 3 ports the rest are 2. I will fix that with a new controller down the road, right now I have blown my budget for this project twice over.

I tested the crap out of the 2 smaller drives they are good.

I am running UD and UD+ (super useful especially during onboarding)

 

So how I have it setup now, I added the 256g and the 250g to the cache. Which resulted in a 253g raid1....which seems wrong to me...

1) I wanted raid 1 for protection from a drive failure.  Is it using the extra 6 gig on the 256 as 2x 3gig? How does it do that? However I was thinking. I have the min free space set to 4.7g so if that 'extra' 3 gig is at the END of the drive then it does not hurt me and actually helps me.

Origionally I was planning on running the 500g alone and using it as a vm/docker/system store. Leaving the 250ish as the write cache and calling it a day.

 

But other configs have occurred to me.

2) Would it be beneficial to raid 0 the 256 and 250, and then raid 1 that to the 500. I dont want to lose unraid monitoring of the drives so I was thinking the raid 0 would have to be software too. But this would way simplify management, I'd just set the shares to cache only and bobs your uncle. This also gives me raid 1 protection of the vm store. Since I'd be mixing sata 2/3 for now and old/new drives it'd be giving up a lot of of performance...but these are vms on ssds, its already going to be way quicker then my 15k rpm drives/SAS1 drives I'm coming from. This would also give me a much larger write cache when the active vm store is small. (I'm using a plugin that backs them up to the array nightly. My intension is just to delete them when I'm not using them and depend on the backups if I want them back.)

 

Also debating on which drives to put on the sata3 ports, right now I have the 2 cache drives on it and the 500 on sata2 but the 500 is still running smart tests etc.

 

Thoughts?

 

 

 

Edited March 17, 2020 by Madoc

[JorgeB]

3 minutes ago, Madoc said:

So how I have it setup now, I added the 256g and the 250g to the cache. Which resulted in a 253g raid1....which seems wrong to me...

https://forums.unraid.net/topic/46802-faq-for-unraid-v6/?do=findComment&comment=480420

 

 

4 minutes ago, Madoc said:

2) Would it be beneficial to raid 0 the 256 and 250, and then raid 1 that to the 500.

You can't do that, all raid1 or all raid0, you can have a raid1 pool plus 500GB unassigned single device.

[Madoc]

Thank you that thread not only answered #1 but also the additional questions that answer raised

 

2) There are ways to do it. I could use hardware to raid 0 the 2 drives. Then Unraid would see a 506 and a 500 and raid 1 them to a 500.

Or I've seen people talking about using other tools (mdadm)  to do linux software raid, so mdadm software the raid 0 and the rest is the same.

Might not be able to do a raid of raids with btrfs but there are ways. 

What I'm wondering is would be benificial. Or am I just buying myself headaches.

 

The raid1 pool and the 500 in UD is what I was thinking before and if it turns out my new idea is impractical or inadvisable thats the way I'll go.

[testdasi]

Stick to RAID-1 pool + 500 UD.

 

You can't do that kind of nested RAID (not that it's even recommended).

Also RAID-0 is highly NOT recommended to new users due to their inability to appreciate the risks involved.

 

Simplicity is an underrated value.

Edited March 18, 2020 by testdasi