ZFS Datastore - Fragmentation with SSD ?


Renowned Member
Feb 3, 2015

I have recently replaced all my HDD for 10 SSD for my ZFS Datastore.

This is now extremely fast specially verify jobs (even if we can discuss the interest of verifying snapshots on a ZFS pool).

The weird thing is that PBS reports fragmentation on the related pool :


AFAIK, on a SSD pool, there is no fragmentation ?
AFAIK, on a SSD pool, there is no fragmentation ?
Well, definitely something I would not worry about with SSDs, even if ZFS reports some fragmentation. It still sees that the data is fragmented across available space of the SSDs.
In the context of SSDs, all writes are "fragmented" by design by the storage controllers on/inside the NVMe/SSDs

In the context of ZFS it's the ZFS that was not able to find a contiguous block of size Y and had to split it in smaller chunks (ashift size) and spread that all over the storage. Something that is more frequent as your ZFS pool usage nears/goes over the ~10-20% free space available mark and ZFS then spends more time to find blocks closer together to each and splitting up blocks, so yes, there is a performance impact, just not direct I/O related, but suddenly instead of a single Y block transfer, you now issue Nx ashift size IO requests and increasing the IOPS needed


The Proxmox community has been around for many years and offers help and support for Proxmox VE, Proxmox Backup Server, and Proxmox Mail Gateway.
We think our community is one of the best thanks to people like you!

Get your subscription!

The Proxmox team works very hard to make sure you are running the best software and getting stable updates and security enhancements, as well as quick enterprise support. Tens of thousands of happy customers have a Proxmox subscription. Get yours easily in our online shop.

Buy now!