Solid State Disk as Oracle storage

I recently completed a cool project: implementing 11g release 2 RAC on Solid State Drive (SSD). SSD is still too expensive except for the most advanced systems. With $10/gigabytes price tag, it is about 20 times more expensive than Hard Disk Drive (HDD). But it is fast, quit, more durable and greener with 90% less power consumption. It is projected that SSD will cost only few dollars per gigabytes within two years and likely will replace HDD like USB flash memory did to floppy disk.

In the blog, I present the IO testing result of SSD against SAN using ORION (Oracle IO Calibration tool). ORION result is more closely mimicking of Oracle database IO characteristics.

Large read throughput for SSD is at 116 MBPS (MegaBytes Per Second) vs. 40 MBPS for SAN. The transfer rate is much less than theoretical transfer rate of SDD and SAN but it is likely the throughput Oracle could achieve for such hardware. It is worth to note that SSD is only mirrored by not stripped, and SAN is mirrored and stripped. So it is reasonable to assume SDD throughput would be few times faster if it were in RAID 01 configuration. I use the same configuration of SAN and SDD of large read for all other tests as well. The random small read throughput for SAN is 1.8 MBPS or 225 IOPS (IO Per Second). The random small read throughput for SSD is 72 MBPS or 9000 IOPS, which is 40 times faster than HDD. Because SSD removes the latency to move the disk head to new disk sections, the random small reads is about 60% the speed of large read for SSD. The data suggests SDD is great for OLTP system and for control file and redo logfile of Oracle database.

Large write throughput for SAN is 79 MBPS and 160 MBPS for SDD. Small random write for SAN is 22 MBPS or 2750 IOPS. Small random write for SSD is 79 MBPS or 9875 IOPS. It is interesting to see that write IO performance is better than read for both SAN and SSD. My guess is that storage write forward cache play significant role here and it is hard to measure true disk write speed. However, it is clear that SDD outperformed SAN once again.

First Impression of Oracle 11gR2 RAC

11g Release 2 RAC has some major changes from 11g Release 1.

For starter, ASM and Clusterware are combined into single Oracle binary home called Oracle grid infrastructure. By default, the voting disks and OCR are in ASM diskgroup instead of raw devices recommended in previous releases. Such change contradicts the concept that ASM is on top of clusterware for previous releases and raise question such as, if ASM is crashed, does clusterware service dies as well because voting disks and OCR are not accessible? Well, the clusterware can access voting disks directly without going through ASM, so it will bring up ASM automatically after it is crashed. Restore an OCR is more difficult and requires to shutdown clusterware on all nodes, then start clusterware on one node exclusively with ASM online. Fortunately, OCR is not easy to corrupt because it is in a normal redundancy diskgroup or high redundancy diskgroup.

Another new feature of 11g Release 2 is SCAN (Single Client Access Name) which binds round-robin dynamic DNS to RAC nodes. It provides easy way of load balance and failover for any client connection. However, it could be a challenge to setup DNS and I wish the installation can have an option not to use SCAN for RAC.

Overall, release 2 RAC is easier to install and deinstall than that of earlier release and more stable because of cluster time service. It also has better scalability than earlier release because the performance improvement of inter-node communication.