Can you use multiple SSD for L2 cache?

rrbnc · Thu Dec 04, 2014 4:16 am

Is it possible to use multiple SSD drives for L2 cache? For example, instead of purchasing a more expensive 1.6 TB Intel P3700, is it possible to purchase two 800 GB Intel S3700 SSDs and get 1.6TB of L2 cache that way?

AndyKnight · Thu Dec 04, 2014 9:58 am

You can do that, I'm doing it with my lab build here. I have 2 x 128GB SSD's and operate them as independent L2 cache drives using one for one set of volumes and the other for a second set of volumes.
You could RAID 0 them together if you want one big pool of cache space but then you increase the chance of a SSD failure removing all L2 cache functionality from all volumes when/if one SSD fails. Keeping them as separate drives minimizes the impact of any one SSD failing as far as I am concerned.

Andy

Fri Dec 05, 2014 4:42 pm

Currently you cannot have separated SSDs to cache one LUN within StarWind. What you can do you can configure a software RAID in Windows from your SSDs and use resulting virtual volume to host StarWind cache file on

AndyKnight · Sat Dec 06, 2014 10:07 am

I'd rather keep the cache drives as separate entities to limit the perf impact if any one failed. At least then you can lose a cache drive and only a subset of your volumes lose L2 cache functionality.

Mon Dec 08, 2014 8:55 am

For now that' the working plan for us: per-VM exclusive L1 caches and deduplicated per-data store L1 and L2 caches (shared). We'll see

AndyKnight wrote:I'd rather keep the cache drives as separate entities to limit the perf impact if any one failed. At least then you can lose a cache drive and only a subset of your volumes lose L2 cache functionality.

Mon Dec 15, 2014 2:56 pm

OK, so am I correct in understanding that you want to use >1 Flash drive as the L2 cache of one single StarWind device?
May I wonder what implementation scenarios do you see with that? BTW I have already informed R&D about your feature request.

barrysmoke · Tue Jan 06, 2015 5:02 pm

Anatoly,
I didn't read into any of the posts that they want to dedicate a drive to a single device. I would like to speculate, that this might be a good place for lsfs on raw device, instead of ntfs on top. the cache drive would be able to bypass the ntfs filesystem overhead, i fit were allowed to be a raw device, and starwind placed lsfs on top of it. I also could see using this pool for multiple starwind devices, maybe assign a set of globaly available cache devices, and upon target creation, pick which one to use.

Mon Jan 12, 2015 11:16 pm

It is. I will make sure that this will be reported as the feature request to our R&D. Thanks for sharing your idea!