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Caching Almost all hard drives (SAN, standalone) have some form of caching (RAM in front of storage) For SQL Servers—make sure you have a battery backed cache—if you don’t and power fails—you will lose data!
Disk Drives Hard Drives can only spin at 15,000 RPM. Hard Drive Performance has improved approximately 50x Have grown in capacity During the performance improvement CPU speed increase 5521x
Latency ―Disk latency is around 13ms, but it depends on the quality and rotational speed of the hard drive. RAM latency is around 83 nanoseconds. How big is the difference? If RAM was an F-18 Hornet with a max speed of 1,190mph (more than 1.5x the speed of sound), disk accessspeed is a banana slug with a top speed of 0.007 mph.‖--credit Christian Paredes Blue Box Group
CPU and Disks As CPUs have gotten faster they have the ability to drive more IOPs. Modern CPUs are so powerful they can saturate a 10 GB connection with I/O requests—your disks can’t possibly keep up
SSDs are Fast Much faster on random reads and writes At least 5x better performance, often much more Up to 350x faster on seeks Not nearly as much of difference on sequential reads and writes
SSDs are Expensive List Prices From Fusion-IO 160GB SLC ioDrive - $8495 320GB SLC ioDrive - $15495 320GB MLC ioDrive - $7495 640GB MLC ioDrive - $11495 320GB SLC ioDrive Duo – 16,990 640GB SLC ioDrive Duo - $30,990 640GB MLC ioDrive Duo - $14,990 1.28TB MLC ioDrive Duo - $22,990 These are really great for TempDB
RAID RAID—Redundant Array of Independent Disks Hard Drives Will Fail, RAID is what gives you protection from that
What is a SAN? Basically a specialized computer for storage Computer, Switches and Hard Drives Not a performance device Can be used for redundancy and DR purposes Will serve many servers—so critical piece of your infrastructure
SAN Components HBA (Fibre) Card—Connects your server to SAN via Fiber Optic cable iSCSI Card—Ethernet Card connecting server to SAN Switch—Either fibre or ethernet switch connecting server to SAN SAN head unit—Controls processing, RAID levels Disk Array—The physical array behind your SAN (a bunch of hard drives)
iSCSI vs Fibre Channel iSCSI is cheaper, and in smaller shops your network admin can manage the switches Over 10G Ethernet iSCSI is faster, but that is still uncommon Fiber is more susceptible to breakage, but currently more common Fibre is faster, generally Note—all SAN components must be the same speed, or network traffic reverts to slowest in chain
Multi-Pathing How your SAN admin sleeps at night! Make sure your databases servers are multi-pathed
SAN Benefits Expand Capacity easily and on the fly High availability Disaster Recovery
SANs and DR WARNING!—Don’t try this unless you have a real budget and a good SAN admin Most SANs vendors have as an option SAN replication Allows for multi-site failover Multi-site clustering fully supported in SQL Server 2012 Expensive—requires fiber connection between sites and expensive software
SAN Terms LUN—Logical Unit Number, but in practical terms, what your SAN admin will call a disk that he presents to your server Fibre Channel—Fiber Optic connection to SAN HBA Card—Card that plugs into your server to connect it to the SAN IOPs—I/O Operations Per Second—the way your SAN admin measures performance
SANs and SQL Server—What to ask for TempDB absolutely needs its own disk (and you should have multiple TempDB files) Logs should be on a separate disk from data files Ideally separate system and user DBs If shared instance, put split high utilization DBs onto separate disk devices