Recommended sizes and benchmarks for CacheCade volumes

[anomaly]

I haven't found much information regarding CacheCade volume sizes, and how different sizes for CC volumes can impact performance, favorably or not.

Can anyone throw some light on this?

 

[Mike W]

I am sure there is a limit to how large a cashe-cade volume can be and I want to say it is aroud 2TB but that is alot considering what it does. The thing about it is it doesn't work like the cashe' on the controller card by buffering to compensate for slow drive writes or spin up times. It recognizes small sections of data that is being accessed most and moves it to the ssd. This takes the work load off of the controller and drive array and places on the SSD.
Here is a link to a paper that explains it pretty well. Hope this helps
ftp://relier.concepto.ch/Hardware/Drivers/LSI/LSI-CacheCadePro-2_FAQ_US-EN_080811.pdf

 

[mrkrad]

You want to use about 10% of the volume size with redundancy for write-back cachecade in raid-1 since if the ssd fails, your whole volume goes kaput (write-back cachecade 2.0)

 

[anomaly]

You want to use about 10% of the volume size with redundancy for write-back cachecade in raid-1 since if the ssd fails, your whole volume goes kaput (write-back cachecade 2.0)

I was under the impression that the volume loses the write caching capabilities from CacheCade and the CC turns into a read cache only, or so I recall from the documentation. And worst case, that the VD/DG simply needed to be disengaged from the CC volume and then it should be operative again.

Is this correct?

Right now for a 4 x 6TB HGST Deskstar NAS RAID-10 volume I am using two 232G SAS3 (12G) SSDs. 10% of 10.9TB is over 1TB. I don't have any higher capacity SAS SSDs available/free to use, and I feel like grabbing two 400G or 800G SAS SSDs is a waste for a CC volume. I do have some Intel DC S3700s. Is there a big performance impact between SAS and SATA SSDs for CC?

 

[mrkrad]

SAS is usually faster, dual-ported 6g sas can trasnport 12gbps and 12gbps sas dual-ported can push 24gbps. Just depends on your hot dataset man, the more cachecade the merrier!

If you have it setup for write-back cachecade, i'd just leave it alone!

 

[anomaly]

I was just curious as I have 8 slots only and SAS SSDs come at a premium cost and they are absolutely fantastic for IOPS and concurrent loads. So if I can swap the RAID1 of SAS SSDs (which have SED capabilities and not many of my SAS SSDs support this) for the SATA Intel DC S3700s (400G each), I could save myself those SAS SSDs for actual data storage.