We're setting up a large data store and and would like to use zfs with
some sort of distributed mirroring for disaster recovery. We have 3
"sites" in mind: two machine rooms in one building and one in another
across the street, all connected by GbT networking.
Our thought was to keep 3 mirrored copies of the data, each protected by
Raid-5 (raid-z?). Remote sites would export raw or raid-5/z protected
disk space using iscsi to the central site that would logically host the
data.
Given the size of the data sets (~100TB), 3-way mirroring alone is (on
paper at least) insufficient. Given the number of blocks involved, the
chances of all three copies being bad for *some* logical block are too
large. On the other hand, 6-way mirroring seems excessive. (Our
original concept was to use 4-of-15 erasure coding, so that any 4 of 15
related blocks would be enough for disaster recovery, while each site
would normally hold 5 blocks, allowing for Raid-5 style local recovery
of single failed blocks/disks.)
Questions:
1) is it possible to layer mirroring on top of Raid-Z under ZFS?
2) Is is possible/practical to export raw disks or raid5/raidZ disk
space using iscsi?
3) Are there some other, easier alternatives we haven't thought of?
Thanks in advance.
Jeff Anderson-Lee
Petabyte Storage Infrastructure Project
University of California at Berkeley
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