Gecko Log Structured Storage System (LSSS, or LS3)

The implementation consists of a device-mapper kernel module.
 
 
The Gecko LS3 overlays a log abstraction over a multi-disk RAID
matrix.  All writes are appends to the log. Reads are returned from
the locations on disk which may be anywhere in the log. To save
power, the redundant disks may be turned off, trading off read
throughput for power savings.  For example, in a RAID-1
configuration, all `mirror' disks (but the disk that belongs to the
log head, hence the one that is being actively written) can be
turned off---reads are returned from the `primary' disks. The
scheme generalizes to RAID-5 and RAID-6 respectively. Furthermore,
RAID-5 is superseded by RAID-4, for which the parity disk(s) are no
longer a bottleneck due to the append-only nature of the writes
hitting the log.
 
Since this is a prototype, it does not yet implement live-RAID
recovery.  Ideally, Gecko could be a simple linear layer on top of
the conventional RAID implementations, however, additional
functionality should be available between the layers in order to
maintain efficiency, e.g. the Gecko LS3 layer must be able to put
the disks of the underlying array in various power modes, and to
direct reads to the powered-on mirror disks.