Comment by ryao
4 days ago
ZFS will outscale ext4 in parallel workloads with ease. XFS will often scale better than ext4, but if you use L2ARC and SLOG devices, it is no contest. On top of that, you can use compression for an additional boost.
You might also find ZFS outperforms both of them in read workloads on single disks where ARC minimizes cold cache effects. When I began using ZFS for my rootfs, I noticed my desktop environment became more responsive and I attributed that to ARC.
Not on most database workloads. There zfs does not scale very well.
Percona and many others who benchmarked this properly would disagree with you. Percona found that ext4 and ZFS performed similarly when given identical hardware (with proper tuning of ZFS):
https://www.percona.com/blog/mysql-zfs-performance-update/
In this older comparison where they did not initially tune ZFS properly for the database, they found XFS to perform better, only for ZFS to outperform it when tuning was done and a L2ARC was added:
https://www.percona.com/blog/about-zfs-performance/
This is roughly what others find when they take the time to do proper tuning and benchmarks. ZFS outscales both ext4 and XFS, since it is a multiple block device filesystem that supports tiered storage while ext4 and XFS are single block device filesystems (with the exception of supporting journals on external drives). They need other things to provide them with scaling to multiple block devices and there is no block device level substitute for supporting tiered storage at the filesystem level.
That said, ZFS has a killer feature that ext4 and XFS do not have, which is low cost replication. You can snapshot and send/recv without affecting system performance very much, so even in situations where ZFS is not at the top in every benchmark such as being on equal hardware, it still wins, since the performance penalty of database backups on ext4 and XFS is huge.
There is no way that a CoW filesystem with parity calculations or striping is gonna beat XFS on multiple disks, specially on high speed NVMe.
The article provides great insight into optimizing ZFS, but using an EBS volume as store (with pretty poor IOPS) and then giving the NVMe as metadata cache only for ZFS feels like cheating. At the very least, metadata for XFS could have been offloaded to the NVMe too. I bet if we store set XFS with metadata and log to a RAMFS it will beat ZFS :)
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Refuting the "it doesn't scale" argument with a data from a blog that showcases a single workload (TPC-C) with 200G+10tables dataset (small to medium) at 2vCPU (wtf) machine with 16 connections (no thread pool so overprovisioned) is not quite a definition of a scale at all. It's a lost experiment if anything.
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No doubt. I want to reiterate my point. Citing myself:
> "I personally won't use either on a single disk system as root FS, regardless of how fast my storage subsystem is." (emphasis mine)
We are no strangers to filesystems. I personally benchmarked a ZFS7320 extensively, writing a characterization report, plus we have a ZFS7420 for a very long time, complete with separate log SSDs for read and write on every box.
However, ZFS is not saturation proof, plus is nowhere near a Lustre cluster performance wise, when scaled.
What kills ZFS and BTRFS on desktop systems are write performance, esp. on heavy workloads like system updates. If I need a desktop server (performance-wise), I'd configure it accordingly and use these, but I'd never use BTRFS or ZFS on a single root disk due to their overhead, to reiterate myself thrice.
I am generally happy with the write performance of ZFS. I have not noticed slow system updates on ZFS (although I run Gentoo, so slow is relative here). In what ways is the write performance bad?
I am one of the OpenZFS contributors (although I am less active as late). If you bring some deficiency to my attention, there is a chance I might spend the time needed to improve upon it.
By the way, ZFS limits the outstanding IO queue depth to try to keep latencies down as a type of QoS, but you can tune it to allow larger IO queue depths, which should improve write performance. If your issue is related to that, it is an area that is known to be able to use improvement in certain situations:
https://openzfs.github.io/openzfs-docs/Performance%20and%20T...
https://openzfs.github.io/openzfs-docs/Performance%20and%20T...
https://openzfs.github.io/openzfs-docs/Performance%20and%20T...
What I see with CoW filesystems is, when you force the FS to sync a lot (like apt does to keep immunity against power losses to a maximum), the write performance slouches visibly. This also means that when you're writing a lot of small files with a lot of processes and flood the FS with syncs, you get the same slouching, making everything slower in the process. This effect is better controlled in simpler filesystems, namely XFS and EXT4. This is why I keep backups elsewhere and keep my single disk rootfs on "simple" filesystems.
I'll be installing a 2 disk OpenZFS RAID1 volume on a SBC for high value files soon-ish, and I might be doing some tests on that when it's up. Honestly, I don't expect stellar performance since I'll be already putting it on constrained hardware, but let you know if I experience anything that doesn't feel right.
Thanks for the doc links, I'll be devouring them when my volume is up and running.
Where do you prefer your (bug and other) reports? GitHub? E-mail? IP over Avian Carriers?
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