25 Sep The more arcane tuning techniques for ZFS are now collected on a central page in the -Wiki: ZFS Evil Tuning Guide. Before. Tuning should not be done in general and Best practices should be followed. So get very much acquainted with this first. 25 Aug ZFS Mirrored Root Pool Disk Replacement For potential tuning considerations, see: ZFS Evil Tuning Guide, Cache_Flushes.

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This is mechanical, it’s latency-bound, it’s slow. The size of the separate log device may be quite small. Draft For more cache tuning resource information, see: The syntax for enabling a given tuning recommendation has changed over the life of ZFS releases. Of course, the numbers can change when using smaller RAID-Z stripes, but the basic rules are the same evio the best performance is always achieved with mirroring.

If you look through the zfs 1M man page, you’ll notice a few performance related properties you can set.

ZFS Evil Tuning Guide –

There are cases huide the total bandwidth of RAID-Z can take advantage of the aggregate performance of all drives in parallel, but if you’re reading this, you’re probably not seeing such a a case.

It would be rare to need more than MBytes in a separate log device, but the separate log must be at least 64 MBytes.

Disabling the caches zgs have adverse effects here. There’s no free lunch. There may be scenarios in lower memory systems where a single 15K SAS disk can improve the performance of a small pool of 5. Writes that are only complete after they have been successfully written to stable storage. Again, these different ways of looking at performance can be optimized by different means, you just need to know into which category your particular problem falls.


If your performance problem is really that hard, we want to know about it. This can have a big impact if your application doesn’t care about the time of last access for a file and if you have a lot of small files that need to be read frequently. The zfetch code has been observed to limit scalability of some loads. Because if you don’t have enough free blocks in your pool, ZFS will be limited in its choice, and that means it won’t be able to choose enough blocks that are in order, and hence it won’t be able to create evol optimal set of sequential writes, which will impact write performance.

However, fixed by bugthe code is now only prefetching metadata and this is not expected to require any tuning. There’s also no provision for striping reads across multiple devices. The good news here is gide ZFS automatically turns random writes into sequential writes through the magic of copy-on-write.

These are most often found in file and database servers and these kinds of writes are very sensitive to latency or IOPS performance. Therefore, you should tune the arc.

To increase performance, you may increase kern. Solaris packaging system aka IPS is great, flexible and available on-line, so if you have your support license you’re entitled to download Depending on your workload, it may be possible to use ZFS on systems with less memory, but it requires careful tujing to avoid panics from funing exhaustion in the kernel.


This works both for increasing IOPS and for increasing bandwidth, and it’ll also add to your storage space, so there’s nothing to lose by adding more disks to your pool.

A properly tuned L2ARC will increase read performance, but it comes at the price of decreased write performance. In a way, this is the roadmap that ZFS needs guife find its way through your disks and the data structures there. Jose about tar -x and NFS – or: For reads, the difference is even bigger: This is slower than necessary, and you really want to avoid that.

A 5x performance difference!

Ten Ways To Easily Improve Oracle Solaris ZFS Filesystem Performance

The pool essentially magnifies writes by writing them to the pool as well as the L2ARC device. In the utter majority of all ZFS performance cases, one or more of 1- 8 above are almost always the solution.

One less class of performance problems to take care of. But a mirrored pair of disks is a much smaller granularity than your typical RAID-Z set with up to 10 disks per vdev.

That’s just how the numbers play out.