Heterogeneous pool with Raid 5 SSD and Raid 5 SAS 15K

Assuming you accounted for the recommended ratio of hot spares, while a 2+1 RAID 5 tier of SSD's doesn't line up exactly to our recommended multiple for RAID 5, sometimes you work with what you have.  Yes, to answer your question directly, RAID 5 (2+1) is supported and is also the minimum size for a RAID 5 raid group.  Keep in mind, you can certainly benefit from even a small tier of SSD's in a pool and in most cases can be much better than not having any SSD's in the pool; in particular, if using thin LUN's (TLU's) as the resulting metadata acceleration improves the overhead associated with the 8KB granularity (when compared to Thick LUN's (DLU's) or traditional LUN's).

Keep in mind, to keep the level of performance consistent for the "Extreme Performance" (SSD) tier, you will then want to understand the underlying private RAID group constructs as your choice on how you initial create the tier influences your new "best practice" (note the quotes) when you expand that tier in the future.

Also, keep in mind with SSD's you have another option (assuming you have the license) which is FAST Cache.

Your question is similar to the following post where each of the above are discussed in a little more detail.

https://community.emc.com/message/737450#737450

As for a document about general best practices, you will want to start with the following:

https://support.emc.com/docu42660_Applied_Best_Practices_Guide:_EMC_VNX_Unified_Best_Practices_for_Performance.pdf

Thanks Chris , Idea would be not to use FAST Cache for all the storage pools , at some point it will be at threshold in terms of IOPS . I was planning to use few storage pools ( heterogeneous ) with SSD and SAS 15 K ( for Datastores in Vmware for DB's etc)  . This way they will be auto tiered and using SSD for faster data and SAS for tier two stuff and still can meet the IO requirements etc . Please advise if this is reasonable planning wise , do I need to have FAST VP license to meet this requirement ?

Appreciate your response.

EMC recommends first utilizing available Flash drives for FAST Cache, which can increase performance for all LUNs in the system. You can then tweak  performance as needed with additional Flash drives in storage pool tiers. Data in the SSD drives will not be put into fast cache.   The minimum amount of  fast cache drives on a VNX 5700 should  be 8.

Spread the EFD drives across all available buses and dont  use  Bus 0 ENC 0

Chris , That's good to know , our EFD Flash drivers are in Bus 0 en0 , this is brand new so if I understand it correct , you would want me to replace the existing 2 EFD with spare and move them to Bus 0 ENC 1 and then if I am scaling FAST cache I will add multiples of 2 in each Bus and spread them out  ?

Please advise if this is ok?

ASR , Can you please explain the power failure issue ?

You don’t want to have Fast Cache RG spread between 0_0 and another ENC , if there was a power failure 0-0 is protected

by the SPS’s

Understood , what is the recommended practice ? If I am extending the RAID 10 FAST Cache beyond 2 drives for faster performance ?

You can review the following:

emc251589: "FAST Cache configuration best practice"

Let me know if this works -

I will destroy existing RAID 1/0 Fast cache ( In Bus0 EN0 with 2 100GB mirror and 1 spare) , will move them to Bus 0 , En1 and add 4 more EFD 100GB disks in Bus0 , En2 and EN 3 and create a new FACT Cche raid 1/0 using those 6 Disks .

That way there is no Fast cache in Bu0-En0 and also Fast cache is distributed across existing Buses and enclosures.

Is this a good design ?