15TB HDDs: Western Digital Unveils the Ultrastar DC HC620

Re:15TB HDDs: Western Digital Unveils the Ultrastar DC HC620 by jmpman on Tuesday October 30, 2018 @01:25PM (#18339088)

CRUSH algorithms are used to overcome rebuild limits in modern arrays. https://www.ssrc.ucsc.edu/Papers/weil-sc06.pdf

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Re:15TB HDDs: Western Digital Unveils the Ultrastar DC HC620 by kdkeyser on Tuesday October 30, 2018 @04:40PM (#18341089)

CRUSH is an example (and not the first) of a "distributed rebuild" approach: you have an array of N drives (with N large, e.g. 100), and if 1 drive fails, you read in parallel from all (N-1) remaining drives, while distributing the reconstructed data across the remaining available capacity of all (N-1) remaining drives.

In effect, you get the total bandwidth of (N-1) HDD's working in parallel. And the bandwidth of 100 HDD's doing sequential IO in parallel is really massive ( ~ 10 GB/s).

Examples of companies claiming to use this approach are Qumulo (rebuild in couple of hours), Infinidat (couple of 10's of minutes), ClusterStor GridRAID (now part of Seagate I think), or "Declustered RAID" in GPFS (IBM)

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Re:15TB HDDs: Western Digital Unveils the Ultrastar DC HC620 by pinewurst on Tuesday October 30, 2018 @07:27PM (#18342114)

GridRAID is owned by Cray now, who were the primary OEM from Seagate.

Thanks for pointing out that declustered/distributed rebuild RAID has many historical precedents (also 3PAR BTW) pre-CRUSH/Ceph.

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