Metadata VDEV to speed up Storage Pool and serving media

TrueNAS General
1

I have a storage pool made up of 3x data Vdevs with 22tb drives. Usable capacity 457.07TB. I use it mostly for media. I was wondering if I add a metadata VDEv will I see improvements in performance? I am serving the media with jellyfin and plex.

I am thinking of using my 2tb 870evos in striped for the metadata Vdev.

My system is the following:
ProxMox:
Dell Percision 7920 Rack
1024gb DDR4 2400 MT/s
2x Intel Xeon Silver 4210R
Intel X710
RTX A4000
30x WD Red Pro 22tb
1x Seagate 22TB IronWolf Pro
4x Samsung 4TB 870 EVO
4x Samsung 2TB 870 EVO
2x 4tb Western Digital WD Black SN850X (housed in Dell 6N9RH Ultra-Speed Quad NVMe M.2 PCIe x16 Card) Running VM’s on this in proxmox - ZFS pool striped
TrueNas Scale ElectricEel 24.10 virtualized in Proxmox
I am passing the following:
2x Intel(R) Xeon(R) Silver 4210R CPU @ 2.40GHz 15 cores (30 total)
512gb DDR4 2400 MT/s
LSI 9300-8e card connected to 3 disk shelves with
31 - 22tb harddrives
Data VDEVs 3x RAIDZ2 | 10 wide
Spare VDEVs 1x | 1 drive
PERC H740P
4x 4tb SSD
4x 2tb SSD

2

A Special Allocation Class vDev, (sometimes referred to as Metadata vDev), is a permanent part of a ZFS pool and can not be removed if their are any RAID-Zx vDevs.

Further, striping a Metadata vDev / Special Allocation Class vDev is a very poor idea, as loss of such will cause loss of the entire pool. Regardless if the data vDevs are RAID-Zx or Mirrors. In fact, it is recommended that any Special Allocation Class vDevs have the same disk level redundancy as the data vDevs. So, a RAID-Z2 data vDev can loose 2 disks without data loss. Thus, a Special Allocation Class vDev should be a 3 way Mirror.

However, a L2ARC vDev setup as a Metadata only is both easy to do, can be striped and is not critical to the pool. Meaning on loss of L2ARC vDev device, their is no data lost, just a bit of speed. Plus, if you change your mind, easy to remove.

As for how you setup a L2ARC for Metadata only, easy, change all your Datasets that you want to not cache data to;
secondarycache=metadata

Now will this help your media access?
Don’t know.

1 Like
3

mistyped I meant mirror. so 1 vdev 4 mirrored drives.

4

With 1 TB RAM your metadat is hopefully in ARC already…
For a special vdev to provide any improvement you’ll need to rewrite eveything so that metadata and small files end up where they should.
A persistent L2ARC would fill up over time, and is removable. I suggest trying that first.