Hello Guys,
Does metadata has any impact on the performance in terms of transfer speeds when copying to or from NAS?
Metadata in your RAM (i.e, ARC) will improve your file listings, browsing, and overall snapiness.
More RAM = more room for ARC = more metadata can be loaded and stored in your ARC
Adding a “metadata drive” (which I think you mean a special vdev? L2ARC vdev?) should only be entertained if you can get better performance by upgrading your RAM or adjusting a tunable.
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Yes, the special vdev.
Then the above applies. Keep in mind that you cannot remove a special vdev after it’s already been added.[1]
With special exception to an “only mirrors” pool. ↩︎
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Plus, it better have the same level of redundancy as the rest of the pool. If you add a single drive as special vdev to an otherwise redundant pool, and that drive fails, the data in your pool is toast. It is (like so many things in ZFS) not a cache.
I use it with Samba servers for a larger (~20) group of Apple Time Machine users and the general perception is that it works well. I have not done any “hard” benchmarks.
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Yes, yes. Aware of that.
Beside the directory trasversing, browsing, does it really makes any improvement in the file transfers?
Oh, yes. You’re absolutely right. I think 2 way mirror is good. Can we call it safe choice? Or say 2*2-Way Mirror. A total of four disks. If one dies, spare drive can be added to it.
Nice. I think for servers holding TM backups, its really necessary unless you’re on SSD data disks.
Lately, i’ve been noticing that it takes too much time to browse or when previewing the files or calculating the file size so i plan to implement that. So, what kind of drive is recommended for metadata/special vdev? Like PLP, etc. In addition, how do i determine what disk capacity do i need for the metadata/special vdev? I’m open to Intel/Solidgm, SK Hynix, Micron. Would prefer Gen4. Just don’t want Samsung due to the issues i have read on internet.
Also, is special vdev/metadata drive still required in case of flash based NAS? Like SATA SSD or NVMe/U.2 etc.
And at last, for the pools where the data already exists and if i want to implement the metadata/special vdev, will all the metadata moved to this new special vdev or just the new one? If latter the case, is there any way to move all the metadata safely to this new special vdev?
Rather 3-way mirror. Redundancy is more important than capacity.
For browsing, a persistent L2ARC for metadata does the trick without additional constraints on redundancy, and is reversible. Special vdev further speeds up writes.
Nothing fancy here. PLP not needed. But redundancy, redundancy and redundancy. (Obviously, high endurance cannot hurt.) Preferably no QLC as the drive will do lots of small writes.
What would you try to achieve by speeding up what is already fast? The whole point of a special vdev is to be faster than the rest of the storage.
Only new data. To populate the special vdev, destroy and restore from backup or run a rebalancing script.
A metadat L2ARC would be populated over time just be reading the data.
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