We consider the performance of all the units generally acceptable, though. Several factors caused the bottleneck, including size and nature of the files, disk drive transfer rate, and the overhead of the SCSI command protocol. Another way to boost performance is to split the drives over multiple channels. For the Read During Rebuild test, we simulated a disk failure and measured each system's performance during a data rebuild. The GigaBank and Enterprise turned in poor results, each showing roughly a 60 percent speed decrease.
Sheer throughput is only one measuring stick for the devices, though.
This simulated the workload of a server application run in the real world. 8K block size requests were made randomly with 67 percent read and 33 percent write operations, simulating small, random data transactions. Such numbers reflect the efficiency of the U1's algorithm, which processed requests and transferred data very quickly. We attribute the speed to the size and dynamic nature of the cache on the Compaq SCSI adapter, and the use of read-ahead cache, which predicts read requests and stores them in memory for fast access.