Hello, I've seen posted that expected write speeds for unraid are arount 50MB/Sec with no cache. I also understand that there is a "reconstruct write" feature that can improve this. Before I make an investment in hardware to run unraid, I'd like to have an idea of what I can expect. Can you let me know roughly what speeds are expected with four reasonably fast 7200RPM HDDs in dual-parity mode (say, WD DC HC530's, which can write at ~270MB/Sec) in both standard write mode and in reconstruct write mode, assuming that a decent SATA controller is being used?

50-70MB/s in normal mode, close to 270MB/s with turbo write when the disks are empty, they will slow down as they fill up.

One more Q -- Is it possible to enable turbo-write with invalid parity (eg, a new array with parity sync paused), or will it always default to normal mode? I ask because I was experimenting around with this using a kind of jank setup (USB HDDs), and I was getting ~70mb/sec with reconstruct_write on, and I'm wondering if it was due to the poor hardware or the lack of valid parity.

2 minutes ago, rheumatoid-programme6086 said:

One more Q -- Is it possible to enable turbo-write with invalid parity

No, just with a valid parity (no parity installed will also give you similar speeds).

On 8/14/2023 at 1:51 PM, JorgeB said:

50-70MB/s in normal mode, close to 270MB/s with turbo write when the disks are empty, they will slow down as they fill up.

 

Thanks for your insight. Due to your feedback I switched from a 4-bay USB HDD DAS enclosure to installing a 6x sata adapter in an NVME slot (I'm hosting on a mini PC to reduce power consumption) and I'm now getting 270MB/s writes. With the USB enclosure, I was maxing out at ~170MB/s with two parity and one data drives. For anyone who finds this via Google, the top USB enclosure on Amazon (Mediasonic ProBox HF2-SU3S2) was terrible and maxed out at ~50MB/s regardless of mode & didn't properly pass through drive serial numbers (although some sketch firmware that I found online fixed that). The Terramaster D4-300 was faster, had a better topology (4x separate controllers tied to an internal USB hub), and properly passed through serial numbers ... but was still a big bottleneck. If you don't have SATA on your motherboard or a PCIe slot, an NVMe-to-SATA adapter is definitely the way to go.

@rheumatoid-programme6086 A bit late to this, but just wondering exactly what you did to run unRAID after you switched from the USB HDD DAS enclosure. You mention the 6x SATA adapter in the NVME slot, but since you're running a mini PC, where do the hard disks go? (I'm assuming the mini PC is one of those small ones that don't have any HDD slots, like this HP Elite Mini 600 G9 Desktop PC.)