I have noticed significant storage amplification for my zvols; that could very 
well be the reason. I would like to know more about why it happens. 

Since the volblocksize is 512 bytes, I certainly expect extra cpu overhead (and 
maybe an extra 1k or so worth of checksums for each 128k block in the vm), but 
how do you get a 10X expansion in stored data?

What is the recommended zvol block size for a FreeBSD/ZFS guest? Perhaps 4k, to 
match the most common mass storage sector size?

    - .Dustin

> On Dec 1, 2017, at 9:18 PM, K. Macy <km...@freebsd.org> wrote:
> One thing to watch out for with chyves if your virtual disk is more
> than 20G is the fact that it uses 512 byte blocks for the zvols it
> creates. I ended up using up 1.4TB only half filling up a 250G zvol.
> Chyves is quick and easy, but it's not exactly production ready.
> -M
>> On Thu, Nov 30, 2017 at 3:15 PM, Dustin Wenz <dustinw...@ebureau.com> wrote:
>> I'm using chyves on FreeBSD 11.1 RELEASE to manage a few VMs (guest OS is 
>> also FreeBSD 11.1). Their sole purpose is to house some medium-sized 
>> Postgres databases (100-200GB). The host system has 64GB of real memory and 
>> 112GB of swap. I have configured each guest to only use 16GB of memory, yet 
>> while doing my initial database imports in the VMs, bhyve will quickly grow 
>> to use all available system memory and then be killed by the kernel:
>>        kernel: swap_pager: I/O error - pageout failed; blkno 1735,size 4096, 
>> error 12
>>        kernel: swap_pager: I/O error - pageout failed; blkno 1610,size 4096, 
>> error 12
>>        kernel: swap_pager: I/O error - pageout failed; blkno 1763,size 4096, 
>> error 12
>>        kernel: pid 41123 (bhyve), uid 0, was killed: out of swap space
>> The OOM condition seems related to doing moderate IO within the VM, though 
>> nothing within the VM itself shows high memory usage. This is the chyves 
>> config for one of them:
>>        bargs                      -A -H -P -S
>>        bhyve_disk_type            virtio-blk
>>        bhyve_net_type             virtio-net
>>        bhyveload_flags
>>        chyves_guest_version       0300
>>        cpu                        4
>>        creation                   Created on Mon Oct 23 16:17:04 CDT 2017 by 
>> chyves v0.2.0 2016/09/11 using __create()
>>        loader                     bhyveload
>>        net_ifaces                 tap51
>>        os                         default
>>        ram                        16G
>>        rcboot                     0
>>        revert_to_snapshot
>>        revert_to_snapshot_method  off
>>        serial                     nmdm51
>>        template                   no
>>        uuid                       8495a130-b837-11e7-b092-0025909a8b56
>> I've also tried using different bhyve_disk_types, with no improvement. How 
>> is it that bhyve can use far more memory that I'm specifying?
>>        - .Dustin
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