Figure 34 - Win2K two disk hardware RAID1 random IOs per second. By scheduling read requests to both drives, a two disk TwinStor RAID1 array shows better performance than a two-disk RAID0 array. However, write performance is only that of a single disk as both disks are utilized during writes in order to mirror the bits, so the parallelism offered by the second drive is lost. The RAID0 array is not subject to this constraint, so it is able to take advantage of the additional disk.
As shown in Figure 35 below, the overhead measured for hardware RAID1 is similar to the overhead for a single disk. This is as expected as hardware RAID1 offloads the additional RAID1 processing onto the 3ware card requiring additional processor cycles. The fixed cost for a single disk was 57s, while the marginal cost was .53s per KB read and .42s per KB written. A RAID1 set had a fixed cost of 57s, and a marginal cost of .55s per KB written and .60s per KB read.
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Figure 35 – Win2K hardware RAID1 overhead. Hardware RAID1 has similar overhead to that of a single disk. This is as expected as hardware RAID1 offloads all processing onto the 3ware card rather than burdening the processor.
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To repeat, as suggested in Table 6, the next generation of 3Ware host-bus adapters and drivers improve on many of these results.
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