Expected benefits of read-only NVMe cache?

Synology
,
1

First, I’d like to say thank you to spacerex for your channel. I’ve learned so much about network-related topics there, it’s ridiculous!

Now, on the topic of ssd-caching. It is a little unclear to me which situations having a NVMe cache (specifically read-only cache) will be of benefit, so I need some advice.

Will a RO ssd cache help with things such as:

  • viewing frequently visited directories that contain many thumbnailed photos?
  • opening actual photos (~25MB, ie. above synology’s definition of “small file size” of 1MB)?
  • browsing in plex?

If any of these scenarios benefit from having a NVMe RO cache, would a 1TB drive be better that a 500GB one? (assume photo library of approx 4TB)

2

So for the most part 500 gigs should be enough for pretty much most SSD caches. It will end up with all the databases that are accessed often.

  1. ~slightly not too much
  2. Probably not at all (other than having the NAS not doing other things)
  3. Yes for sure!
1 Like
3

Only one thing to add: if you ever go for a read-write cache one day, you should use larger SSDs, because write speeds are slower for smaller capacities. (Of course, the choice also depends on your network speed: the fastest SSD won’t help if your network connections are slow.) Read speeds, however, are afaik not affected by capacity, so a 500GB drive should be OK, as @Will already wrote. It will just take a wee bit longer for the system to transfer frequently accessed files from your storage pool to the read cache, but I assume that’s barely noticeable, if at all.

1 Like
4

Thank you!

If I may ask a couple of follow up questions:

  • I’ve started a SSD cache advisor-job. Will the result of this analysis indicate anything about the potential benefit of installing a RO cache?
  • Is there any extra risk of installing a healthy five year old NVMe drive as a RO cache? (I’ve already purchased a new 1TB drive, but I’m considering putting it in my computer as a regular drive instead. The old NVMe (512GB) from my computer would then go into the NAS).
5

I don’t know what this SSD cache advisor job is. As for the second question, I’d say: yes, you can put the old SSD into the NAS, because even if it dies earlier, the data won’t be lost, because it’s just a cache using copies of files that are still on your main storage pool. However, I’d run a software first to look at the old SSD’s health. If (for example) you’re already way above the drive’s TBW, I’d probably not use it.

1 Like
6

On the other hand, new 500GB gen3 M.2 SSDs are really cheap now, just a couple of bucks, e.g. the TeamGroup MP34 TM8FP4512G0C101. Even a 1TB model wouldn’t be expensive.

https://www.teamgroupinc.com/en/product/mp34

1 Like
7

Thanks,

The “SSD Cache Advisor” is a job you can start from Storage Manager. It’s explained like this:

SSD Cache Advisor analyzes your current data usage pattern and recommends a suitable size for SSD read-write cache. The initial analysis takes at least 7 days and stops automatically after 30 days.

I’m not sure if this will indicate anything about a RO-cache though, but I guess not :slight_smile: