The Alternative Disk Array Configurations

In addition to the EW-Array configurations, we will experiment with the following alternatives:

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A RAID-10 combines striping and mirroring: data is striped across a number of disks and each of the striped disks is also replicated once.

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A Doubly Distorted Mirror is a variant of a RAID-10. For each logical write request, two ``write-anywhere'' physical writes are performed to free locations near the disk heads. One of these two copies is later ``moved'' to a fixed location in the background [19].

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An SR-Array combines striping and rotational replication: data is striped across $D_s$ disks, and each block is replicated $D_r$ times within a track to reduce rotational delay, so a total of $D_r \times D_s$ disks are used [30].

For configurations that support replication on multiple disks, we shall experiment with two different reliability guarantee scenarios: in one scenario, a synchronous write request is allowed to return as soon as one physical write is committed to a disk platter; in a second scenario, a synchronous write request is not allowed to return until at least two physical writes are committed to two disks. When multiple requests are in the disk queue, the EW-Arrays employ the SATF-EW scheduler discussed in Section 4, and the other configurations employ variants of SATF.