[kwlug-disc] Old Man Yells at ZFS (was: Docker Host Appliance)

[Chris Irwin]

On Thu, Jan 19, 2023 at 12:02:20AM -0500, John Sellens wrote:
>In these days where many machines are VMs, if space is running out,
>you can allocate another disk, attach it to the VM, trigger a (re-)scan
>for new devices, and if you're using LVM, you can pvcreate, vgextend,
>lvextend, and xfs_growfs on a running virtual machine with no disruption.

This is what I've been doing in production for the last 13 years. Data 
grows, and you can easily get surprised at the rate of growth:

* The system ingests PDFs and DOCXs a rate of "x" GB/day
* Allocate enough initial disk for 5 years of growth
* Now including some video with that
* Recalculate with new baseline
* All that new video is HD now...

We're also using xfs, but can cause some pain, too. Relocating a large 
amount of data to a new filesystem (or remote SAN/NAS), you can't 
reclaim any of the space allocated to the existing filesystem, because 
xfs doesn't support shrinking. Every filesystem has it's own unique 
pain.

Arguably, ZFS and BTRFS in the VM is probably overkill anyway. These are 
virtual machines, and data integrity, error correction, and redundancy 
should be handled on the SAN.

>If you're talking physical hardware, some might argue that LVM makes it
>easy to leave some amount of space unused - especially if you have
>multiple partitions - and then add space where needed.

We always leave unallocated space. Aside from being used for snapshots, 
it also gives you breathing room when data filesystems approach full.  
You hit your disk space warnings, you can immediately embiggen the LV, 
while waiting for additional storage to be allocated.

I've seen people asking on reddit about how to make /boot bigger, 
because they made the partition too small initially (and it's usally a 
land-locked partition between /efi and /). Or wanting to carve out some 
space to partition for a second distro. Both are non-issues with LVM.

-- 
Chris Irwin

email:   chris at chrisirwin.ca
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