Install guide

RAID technology

There seem to be more RAID options than ever before. A simple thing to remember for databases

is that, on average, a 144GB 15K drive is the same speed as a 36GB 15K, so if you factor for

IOPS throughput, you don’t need to worry about space.

RAID5 is often used as a speed/space compromise, but is very slow especially for random writes,

which databases do a lot. Sometimes the RAID controllers can hide this effect, but not well, and

not forever. Another common algorithm uses one or more parity drives (most notably Netapp and

HP EVA), and this option is a much better alternative to RAID5.

For database performance, the gold standard is RAID10 (a stripe of mirrored drives), which can

tolerate the loss of 50% of the spindles and keep running at full performance. It might seem like a

“waste” of space, but you are purchasing IOPS/spindle/$; the size of the drive is not relevant to

database performance.

Various RAID options can create extra I/O in order to maintain the persistency, so the actual

numbers of IOPS available to the database (payload IOPS), tends to be less than the spindle

count, as is a function of the selected RAID algorithm.

Shared or non-shared file systems tend to be blocks-based file systems that are constructed on a set of

physical or logical LUNs, as in the case of Red Hat’s Logical Volume Manager (LVM), or the clustered

equivalent for the shared GFS install, CLVMD. An example of a files-based file system would be the NFS

file system. This guide assumes that LUNs are presented for formatting into the appropriate filesystem

type for either Enterprise Edition HA, or RAC.

IOPS Math

There are 3 main factors in calculating IOPS or I/O's Per Second:

Rotational Speed – AKA spindle speed (RPM)

Average Latency – T ime for sector being accessed to be under a r/w head

Average Seek – Time it takes for hard drive's r/w head to position itself over the track to be

read or written.

IOPS is calculated as 1/(Avg. Latency + Avg. Seek)(ms)

Total IOPS = IOPS * T otal number of drives

For example, let's say we want to find the total IOPS in our storage subsystem and we have the

following storage:

4 X 1TB 10kRPM SAS (RAID 0)

Avg. Latency = 3ms

Avg. Seek = 4.45ms

1(.003 + .0045)= 133 IOPS

Total IOPS = 4 * 133 IOPS = 532 IOPS

1.4. Storage Topology and DM-Multipath

Blocks-based clusters still tend to be deployed on Fiber Channel (FCP), but other technologies, such as

iSCSI and FCoE (FCP transport captured into, typically, 10GbE Ethernet) also exist and are supported

Oracle technologies. Device-Mapper multipath is a RHEL service that provides multiple pathways to the

shared storage array. The array is usually accessed through an FCP switch that contains partitioned

Red Hat Enterprise Linux 5 Configuration Example - Oracle HA on Cluster Suite