Skip Sequential I/O option gone?

Hi all,

I bought a Synology DS1821+ around a year ago. I immediately upgraded it with a Synology 10GBe network card and 2 X Samsung SSD980 NVME drives, which I was going to use as a 2TB SSD cache. I also put a 10GBe network card into my video editing PC and mapped a drive across that network to my media share on the NAS. My NAS has 4 X 8TB Ironwolf Pro drives configured SHR1.

Most of my work involves editing multicam, which is HDV, AVCHD and Blackmagic Raw. Of course, I also have proxies flying around and other such workflow things. It all works fairly well, but I did a bunch of testing with the SSD cache when I originally bought the system. Bottom line is, I couldn’t really get the SSD cache to load the data I actually wanted to cache (the media), so it didn’t appear to be caching and I didn’t appear to be gaining any significant performance benefit. So I ditched the 2 SSD NVMe drives and reverted to using just one. It seemed clear to me at this point that NVMe caching doesn’t really do much for sequential performance.

But last night, I checked out some of the older SpaceRex videos and in particular I was looking at the videos about saturating a 10GBe and 2 X 10 GBe network connections, using SSD caching. I noticed there was a setting mentioned in the videos - Skip Sequential I/O. It suddenly occured to me that this setting could be what I need so today I set about trying to find it and untick it, as mentioned in the video. If this is an option to force the NAS to cache big files, it could be exactly what I need.

However, I can’t find this setting in DSM 7.2-64570 Update 3. It seems Synology have removed it. So it’s no longer possible to force the NAS to cache large files.

So I decided to try emulating the testing done in the SpaceRex videos. I can’t get close to them. Firstly, I removed the read only cache and re-added it using just a single NVMe drive. I then copied an 80 Gig video project from the media share to my Windows desktop. Once done, I can see the NVMe cache is now using 1.7 Gb. So no way it’s bothered to cache any of that 80 Gig project. More intruiging still, that 80 Gb copy from NAS to desktop took well over 15 minutes. Not 2 minutes like in the SpaceRex videos. I didn’t bother running the test again to see if it was much faster, because the figures were nowhere near the SpaceRex figures in the video, which tells me something is not right.

So there must be something very wrong here? Or NVMe cache really is no use at all to video editors? Forget the Windows box and the method of copying through a network drive - I’ll work on those potential issues after I can see the NAS actually caching. I’ve run both 1 TB and 2 TB caches and in all the time I’ve owned the NAS, I’ve never seen it cache more than 100 Gig into that cache. My projects are nearly always 500 Gig+ in size and I can have two or three projects on the go at any one time. That’s the problem, I’m sure. I only really use the NAS for video editing and Active Backup for Business currently, so anything in the cache I would expect to be related to video projects.

So what gives?!?

Kind regards, Andrew.