What SSD for my L2 cache scenario?

FAQ, getting help, user experience about PrimoCache
Post Reply
Xyzzy
Level 2
Level 2
Posts: 5
Joined: Mon Sep 30, 2019 12:51 pm

What SSD for my L2 cache scenario?

Post by Xyzzy »

Hello,

I am trying to determine what would be the best SSD for L2 cache for my scenario - seeking generally increased system responsiveness and shortened access times, not any ultra-dramatic changes:
- all data disks (non-boot)
- 1st drive 1.5 TB - "daily computer use" in read/write scenarios. Includes fe. unpacking archives to the same drive and sometimes demuxing movies (writing from fe two 5 GB input files to one 5 GB output file).
- 2nd drive 3 TB - multimedia in read only scenarios - images, movies, music
- 3rd drive 6 TB - games in read-only scenarios (I keep a lot of them, but play just a few in given period).

My starting point would be 128 GB SATA drive. Could I expect any significant improvements with going to 256 GB capacity or NVMe x 2 on PCIE 3 (x4 is not available)? Would I see any improvement from getting some higher end drives (like Samsung EVOs) in given capacity/interface range?

TIA
X.
User avatar
Jaga
Contributor
Contributor
Posts: 692
Joined: Sat Jan 25, 2014 1:11 am

Re: What SSD for my L2 cache scenario?

Post by Jaga »

Hit rate is going to be important in terms of speed gains, which directly depends on the amount of data you are caching. How full are the drives you want to cache, and how much of that data do you use on a regular basis?

As a rule of thumb, I try to get my cache (either L1 or L2) to be no less than 10% of the size of the data I'm caching. Ideally it would even be as much as 20% or more of the data size. Due to the total size of all the drives you have in use, I don't think any single L2 would give enough coverage - unless it was a 1TB or larger SSD/NVme. That would give you enough cache space and a high enough hit rate on all data across all drives.

Your cache is going to be best used on the 1st drive (the 1.5 TB drive), since it is in use the most. As for the games drive - what I would recommend is moving or copying the installs to the first drive and playing them there. If they are Steam games, you can easily accomplish this with Libraries on different drives. After the game is on that drive, it would benefit from the fast L2 caching there and you wouldn't need any cache at all on the 6TB drive.

So the goal really is going to be caching of 1-2 drives only, and using the largest/fastest L2 on it that you can reasonably afford. Caching the other, mostly infrequently used drives, just isn't as effective.

If you add a NVMe as the L2 the responsiveness on the 1.5TB drive would be much greater. Again - I wouldn't go lower than perhaps 256 GB on that size drive, since you want more than 10% data coverage with the size of the L2.

These are just my opinions and personal practices when using Primocache along with a gaming rig that is also used for work daily. Trying to limit realtime use of the drives (i.e. copying/moving games to the 1.5 TB first to be used when playing) is going to help your caching solution.

There are other solutions of course: partitioning your game installs drive so that you have a smaller slice of it for "games being played" to be copied to, and then caching that smaller partition for a high hitrate. It all depends on what you are willing to do, and how much money you can afford to throw at different solutions.
Xyzzy
Level 2
Level 2
Posts: 5
Joined: Mon Sep 30, 2019 12:51 pm

Re: What SSD for my L2 cache scenario?

Post by Xyzzy »

I see, makes sense.

So, assuming I want to cache my "daily" and "multimedia" disks only (both around 75% full; where data set used in some time period is usually limited to tens of gigabytes, and over time slowly migrates to another tens of gigabytes and so on):

- Can I go just with budget Plextor M8V 256GB M.2 SATA (PX-256M8VG)
- Or does NVMe make a difference?
- And how about going into higher end drive with 256 GB?
- Or is lower end in 480-512 GB range better?

I mean I would like to stay in 50 USD range (in US prices).
User avatar
Jaga
Contributor
Contributor
Posts: 692
Joined: Sat Jan 25, 2014 1:11 am

Re: What SSD for my L2 cache scenario?

Post by Jaga »

I wouldn't put a budget SSD on almost any machine, but that's me. I either buy good Samsung SSDs, or Samsung NVMes. Latency and IOPS are going to be important for a L2 drive, so stuck with either a Samsung SSD, or a decent NVMe from someone.

I don't think $50 is going to get you a decent NVMe, so you're stuck with a SSD, probably a 256 GB. There's a Samsung 256 GB on Amazon that's about the right price, but that's not going to get you 10% data coverage on your 1.5 TB + 3TB drives if they are 75% full. It actually works out to 5%. However if you're confident that there's a lot of stuff out there you rarely use, it may be okay.
datahoarder9k
Level 2
Level 2
Posts: 5
Joined: Fri Oct 04, 2019 8:17 pm

Re: What SSD for my L2 cache scenario?

Post by datahoarder9k »

Xyzzy - Here is a crazy link to a hero that looked into SSDs: https://www.reddit.com/user/NewMaxx/com ... guide_wip/
You may also check out anandtech's semi-regularly updated consumer SSD buying guide: https://www.anandtech.com/show/9799/best-ssds

For what it's worth I have a budget intel 660p 1 tb L2 read cache for a seagate ironwolf 10 tb hdd. Only downsides so far are:

1.) intel 660p budget models are bad at switching between suspending write operations in favor of read operations (mixed workloads). I don't really care about this since I'm solely using it as a L2 read cache.

2.) When the intel 660p is near capacity, it will do background processing to flush the SLC cache. This will increase the read latency significantly. I'm considering reserving 5-10% of the capacity (48-96 GB) but honestly I can't find any noticeable slowdowns in day to day tasks so far.
Xyzzy
Level 2
Level 2
Posts: 5
Joined: Mon Sep 30, 2019 12:51 pm

Re: What SSD for my L2 cache scenario?

Post by Xyzzy »

datahoarder9k wrote: Fri Oct 04, 2019 9:54 pmI'm considering reserving 5-10% of the capacity (48-96 GB) but honestly I can't find any noticeable slowdowns in day to day tasks so far.
Do you have the whole disk allocated as L2 cache?
datahoarder9k
Level 2
Level 2
Posts: 5
Joined: Fri Oct 04, 2019 8:17 pm

Re: What SSD for my L2 cache scenario?

Post by datahoarder9k »

Yup: cache task for seagate 9.3 TB 7200 rpm HDD. I think I have about 6.5 TB of data on it:
L1 cache: 4 GB RAM write only
L2 cache: 953 GB read only

Use cases:
some games that aren't on my boot drive
plex/emby home media streaming (photos, music, videos)
shared download folder for my VM seedbox

I've been running the cache task for a few months now, looks like I have around 200 GB free L2 cache. So for my use case, having about 700 GB L2 cache for a disk that is 6,500 GB full seems like a ballpark figure. This ends up with a cache size guesstimate of 11% of the source disk. I'm not sure if that's a figure you can extrapolate to your own use scenario, but I hope it helps.
3 primocache storage drive overview.PNG
3 primocache storage drive overview.PNG (73.19 KiB) Viewed 3029 times
User avatar
Jaga
Contributor
Contributor
Posts: 692
Joined: Sat Jan 25, 2014 1:11 am

Re: What SSD for my L2 cache scenario?

Post by Jaga »

datahoarder9k wrote: Sun Oct 06, 2019 2:58 am This ends up with a cache size guesstimate of 11% of the source disk. I'm not sure if that's a figure you can extrapolate to your own use scenario, but I hope it helps.
Sounds about right to me. :)
Post Reply