STH Forum ZFS Snapshots - guess how much data

[Patrick]

I just wanted to take a quick poll.

STH forums run in their own Ubuntu VM using ZoL with Proxmox/ Debian as the base hypervisor distro. The volume has a total size of 40GB.

Here is my crazy question for you: day to day snapshots how much data changes?

zfs send -nv -i sasarray1/vm-102-disk-1@sthforum20151209 sasarray1/vm-102-disk-1@sthforum20151210
What is the total estimated size ______?

I have to say, I was a bit surprised at first. It does at least give some idea how much data is changing on the disks daily.

 

[pgh5278]

A total wag with no basis - 15GB

 

[mstone]

couple hundred megs?

 

[Jeggs101]

A few logs and a few text database updates. How big could that be? 10MB? 50?

 

[Naeblis]

less than 2mb

 

[TuxDude]

I'll guess in the 2-3 GB range.

 

[canta]

1G on my bet haha!

 

[Patrick]

Ending the suspense - it turns out the forums generate 600MB or so per day of snapshot delta or about 1.5% of the total volume size (but there is a lot of free space.)

 

[Mike Bailey]

@Patrick: What stack are you running for the actual forum software? If I had to guess, it's unlikely the VM itself generates much in the way of anything beyond incremental DB changes and some logs.

Just guessing, logs might be no more than 100 MB a day, if that. Database changes? Easily not a lot. If you look at the actual underlying data files, most DB engines do a very good job of making sure they can make changes in place without having to split the pages in an index.

That being said, 100 - 200 MB of writes to a database, especially if it's new content added on, will only amount to a small amplification factor in terms of disk churn.