Hard Drive Speeds

airborne spoon · February 24, 2022

I'm going to upgrade my plex NAS in like a year (at the speed I'm filling it up at) or so and I'm trying to figure out how to get the best speeds. Right now I have 4x 10TB WD reds in raid Z2 (2x are 5400 RPM and 2x are 7200 RPM). Now I want to add at least another 20TB of storage and logically I'd just buy another 4x 10TB drives and rebuild the entire array. I'd back it up onto a spare drive then build the array and then move all those files over to the NAS. I'm not aware of any other way to do this on TrueNAS since the entire array has to be built at the creation of the thing. I know i can add another pool but that doesn't do anything for the redundancy since its a separate array from the original which from what I've read isn't as safe as building 1 massive array.

Anyway will buying more smaller drives speed up the write speed at all like instead of 4x 10TB drives i got 10x 4TB drives. Or would that just add more potential points of failure?

I have it hooked up to my main PC via fiber 10G line so that is not the bottleneck, its the speed it writes to the drives that is my current annoyance. I can write for 300MB/s for a moment until the drive cache fills and it drops to 7MB/s for a bit then jumps back to 300 and then back to 7 till all the files are written.

I've heard that other NAS solutions you can add storage to the array as you go and also allow for having a cache drive to make write speeds faster. But all I've found are ones you have to pay for or have subscription fees for software you own.

AbydosOne · February 24, 2022

6 minutes ago, airborne spoon said:

I'm not aware of any other way to do this on TrueNAS since the entire array has to be built at the creation of the thing.

You can add VDEVs to a pool. Just add another RAIDZ2 VDEV to your existing one.

6 minutes ago, airborne spoon said:

I can write for 300MB/s for a moment until the drive cache fills and it drops to 7MB/s for a bit then jumps back to 300 and then back to 7 till all the files are written.

This is actually atypical in my experience (same 10G NIC and 20TB RAIDZ2). I can write pretty much indefinitely without hitting limits like that. What hardware are you on?

6 minutes ago, airborne spoon said:

allow for having a cache drive to make write speeds faster

See here.

mariushm · February 24, 2022

Ignore the motor speed, it's irrelevant. The actual throughput of a drive is mostly about data density (how densely packed the data is on the platter) and how many platters there are (more platters means more heads, higher latency because it takes a bit more time for heads to move to a data track)

The read/write speeds are not constant throughout the surface of the drive ... because it depends on the physical location of the track on the platter surface (a track closer to the center will be read faster than a track on the outer edge of the platter) ... so you could have a drive that can write at 300 MB/s at the start and gradually go down in the 100-150 MB/s towards the end of the capacity.

Get drives that use the classic CMR, not the SMR kind. A lot of SMR drives will have a high size cache (ex 256 MB) to counteract the slow writes and rewrites.

Get dries optimized for NAS, or "enterprise" ... that's all.

You could always add a SSD as a write cache drive.. or you could add more ram.

// wd red nowadays are SMR ... well, the <8 TB drives used to be SMR back when they started using SMR and then the s@#t hit the fan and people started complaining and WD released a blog post about it...

Nowadays, they committed to using SMR on WD Red series, and WD Red Plus series is CMR only.

WD at least has datasheets ... here's for example the WD Red Plus : https://documents.westerndigital.com/content/dam/doc-library/en_us/assets/public/western-digital/product/internal-drives/wd-red-plus-hdd/product-brief-western-digital-wd-red-plus-hdd.pdf

You'll see the maximum speed will vary depending on capacity - my guess is some use newer platters which pack data more densely, other models use older generation platters.