Howdy, Stranger!
Categories
- All Categories
- 73 General
- 73 Announcements
- 66.6K Microsoft Dynamics NAV
- 18.7K NAV Three Tier
- 38.4K NAV/Navision Classic Client
- 3.6K Navision Attain
- 2.4K Navision Financials
- 115 Navision DOS
- 854 Navision e-Commerce
- 1K NAV Tips & Tricks
- 772 NAV Dutch speaking only
- 615 NAV Courses, Exams & Certification
- 2K Microsoft Dynamics-Other
- 1.5K Dynamics AX
- 310 Dynamics CRM
- 109 Dynamics GP
- 10 Dynamics SL
- 1.5K Other
- 993 SQL General
- 384 SQL Performance
- 34 SQL Tips & Tricks
- 34 Design Patterns (General & Best Practices)
- Architectural Patterns
- 10 Design Patterns
- 5 Implementation Patterns
- 53 3rd Party Products, Services & Events
- 1.7K General
- 1.1K General Chat
- 1.6K Website
- 79 Testing
- 1.2K Download section
- 23 How Tos section
- 260 Feedback
- 12 NAV TechDays 2013 Sessions
- 13 NAV TechDays 2012 Sessions
Answers
Well, with SAN it's different - and have in mind that not everything which pretends to be a SAN really IS a SAN ...
The problem with RAID10 is, that it is quite expensive, as you have to use the half amout of disks just for the mirroring. RAID5 does not mirror the data, but create Parity Sums (to restore the data if one disk is damaged). The writing of the Parity Sums is degrading the performance of write-transactions, thus not really recommended.
Real SAN (!) are using 20 spindles and more. It would cost a fortune if half of them would be just "wasted" for mirroring. Thus, SAN are usually running RAID5 variants (mostly RAID5DP or RAID6 or vRAID5):
The data is striped over e.g. 18 spindles, and 2 disks are used to write the double Parity Sums.
BUT: with real SAN this is NOT degrading performance, as all physical write transactions are perfromed asynchronously! The Fibre Channel headers provide a large piece of cache - NVRAM - usually 2GB and up. The SAN commits the write-transactions as soon as the data is in the cache - the SQL Server is virtually communicating with a sort of RAM disk. THEN the SAN is asynchronously transferring the data from the cache to the spindles (physical write), but writing the parities does not matter here.
So the short story is: with SAN - real SAN! - RAID levels using parity are not degrading perfromance, as a RAM cache is buffereing the data.
This also means, that Independent Power Supply and proper battery buffers are mandatory!
Many "wannabe SAN" just provide multiple spindles, but no or insufficient cache. With those storag systems a RAID5 & Co. will degrade performance of write-transactions.
As far as I know HP EVA is a "real SAN"
NAV/SQL Performance Optimization & Troubleshooting
STRYK System Improvement
The Blog - The Book - The Tool