ZFS subvolume support inside Bhyve vm

[John Nielsen]

> On Mar 10, 2016, at 5:31 PM, Paul Vixie <paul at redbarn.org> wrote:
> 
> Сергей Мамонов wrote:
>> Hello!
>> 
>> Yes - zvols looks awesome. But what driver you use for it?
> 
> virtio-blk.
> 
>> And what
>> about disk usage overhead in guest?
> 
> ufs on zvol is faster, either in the parent or a bhyve using virtio-blk, than zfs. at least for writing, which is my dominant work load. i expect that this is due to zfs's compression logic rather than anything having to do with creating/extending files to accommodate writes.
> 
>> virtio-blk doesnt support fstrim (ahci-hd support it, but slower? "/At
>> this point virtio-blk is indeed faster then ahci-hd on high IOPS/").
>> In linux && kvm we try used virtio-scsi driver with support fstrim, but
>> how I see it not availble now in 10-2 stable for bhyve.
>> And I not lonely with this question -
>> https://lists.freebsd.org/pipermail/freebsd-virtualization/2015-March/003442.html
> 
> i'm just going to live without fstrim until it's supported in virtio-blk. i know that this option isn't available to everybody, but at the moment storage is cheap enough to waste.

At the risk of getting farther off-topic..

Virtio-blk can't and won't support fstrim. If/when bhyve were to have virtio-scsi support that could work with trim, but last I was aware there wasn't a whole lot of momentum in that direction. The virtual AHCI controller in bhyve does support trim and performs remarkably well. That's what I use for my vol-backed VMs and I haven't had any complaints. Worth testing, IMO.

JN