Flash cache - Image/LSFS - Sizing

[raymondjt]

Hi,

in the early versions of StarWind v8 the "L2 Cache" could only be choosed if the device was LSFS.

On the latest version 8.0.8703 the wizard "Add Device (advanced)" allows the select the "flash cache" for both options: Thick-provisioned and LSFS

Is this a bug or a new feature?

What about the sizing? Best practices for "flash cache"?

Example:
Device lsfs - 1024 GB, 4096 virtual sector size
- recommondation for (RAM) Cache size ?
- recommondation for Flash Cache size?

Any difference if dedup is activated or not?

Thanx
Raymond J. Tuleweit

[Ironwolf]

Your Example is to vague, start by thinking about the data, and how the data is used. Then think about the contention on the physical storage itself, as in how many LUNs are you planning? How busy do you think each of the LUNs is? (the more LUNs/busy the larger the cache you need per LUN, to help hide/absorb contention for the physical storage)

The recommendations I have seen suggest 10% - 10%

Your Example: Drive/LUN Size 1TB (1024GB)
L2 SSD Cache, 10% = (1024 * .1) = 102GB
L1 Ram Cache, 10% = (102 *.1) = 10GB

But it is so subjective its not easily defined by a fix rule. A trick I use in my home LAB only, not suitable for production (don’t do it). Set Starwind to zero L1/L2 cache. Use FancyCache/PrimoCache and play with the cache levels until happy. Some workloads it just doesn't matter, others it makes a huge difference.

[darklight]

I usually treat L2 cache size to be able to cover your "working set" or so-called "hot data". Usually, it is 10%-20% of you total virtualized data, that is why I assume starwind recommends to size it this way. Basically, the same applies to L1 cache also, but it is rather expensive to get 10% of your storage covered by RAM, so starwind recommends to have at least 1% covered for good performance. These recommendations apply to both types of devices but in the case of LSFS, you should keep in mind that it will consume additional RAM for sequentializing and for deduplication. Exact amounts might be found here https://knowledgebase.starwindsoftware. ... scription/ under Requirements and Limitations.

[Tarass (Staff)]

Nice conclusions, darklight.

Anything else I can help here with?