why distinct rpool/tank pools, when tank only for VMs?

[kdog2]

[I know I've read this before, but I can't recall nor find the reason anymore.]

Why have distinct "rpool" and "tank" pools, assuming the "tank" pool is used exclusively for VM block storage? In this case, both pools seem to have identical data-importance, access-performance, power-loss protection, etc. characteristics...

Assuming rpool is a mirrored-pair of NAS-rated SSDs, and tank is a mirrored-pair of the same NAS-rated SSDs, why not merge them a have one pool composed of two vdevs of mirrored-pairs. Same total amount of space, but twice the read-IOPS, right?

K.

 

[sretalla]

You're asking a loaded question there without providing much information about what "rpool" is to be used for.

I can agree that two VDEVs is better than one for block storage and if that's all your server is doing, then sounds like the right approach.

 

[kdog2]

Silly me, I thought that it was commonly understood that “rpool” stood for “root pool” and is where the host operating system is installed.

The only reason I can think of wanting distinct pools is to enabled fresh-installs of the host OS followed by an “import” of the other pool. A fresh install may be needed if the host OS’s “upgrade” process breaks, or otherwise as a general precaution against bit rot.

 

[danb35]

Why have distinct "rpool" and "tank" pools

I'm wondering about the underlying assumption--you're being told this by someone, but who or why isn't clear--but it's highly likely it's in a context separate from FreeNAS. You can calls pools whatever you want, of course, but "rpool" isn't a name that's commonly used in examples for FreeNAS.

 

[danb35]

The only reason I can think of wanting distinct pools is to enabled fresh-installs of the host OS followed by an “import” of the other pool.

Separation of data and code? Protection of data from an OS crash? And no small part of historical inertia.

From back before there was a FreeNAS (i.e., beginning with m0n0wall, its parent project) through the 9.2 release series, FreeNAS was generally installed on a USB stick, loaded itself into a RAMdisk on boot, and only wrote to the boot device when you changed settings. With 9.3, they moved the boot device to being a live ZFS pool, which enables a number of neat features, but the distinction remains.

 

[sretalla]

Feel free to avail yourself of this option, but make sure to read the caveats/warnings about support.

HOWTO: setup a pair of larger SSDs for boot pool and data

Moderator Warning: This HOWTO will damage the ability of your TrueNAS appliance to properly maintain itself, will break the ability to replace failed drives, and may cause problems with upgrades and updates. TrueNAS is not designed to do this sort of partitioning, and the developers are not...

www.truenas.com

 

[HoneyBadger]

The better option is probably to get a different device media for the boot/root pool, and use the 4 SSDs exclusively for the boot pool.

 

[Arwen]

One issue that has not been mentioned, is that a data pool can be used up to 80%. Or more, if it's a mostly write pool, (meaning archival or backup storage).

However, a VM pool with zVols should not exceed 50% used.

But, combining the 4 NAS rated SSDs into one pool may work better. Just understand that VMs may start to get slower due to fragmentation if you exceed 50% used.