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SCOS 7.3 new "hot spare" strategy?
One of our SCv2080s recently experienced two rebuilds in a short period of time, each took about two days to complete (8T NLSAS). I understand one of the new features of SCOS 7.3 is the new hot spare strategy, if there's any hot spare at all. I wonder how much that will increase rebuild speed and if that comes at a cost? Is usable space gonna remain the same when upgrading from 7.1 to 7.3?
Origin3k
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April 23rd, 2019 11:00
Its called "distributed spare". Some/All? Disks reserves a small portition of reserved space for acting as hotspare(s). Which means when a rebuild is needed the reading parity information can be spread/written to multible disks instead onto a single one. This is way faster as the old method.
I have nothing found how much space is reserved or how many "virtual" hotspaces the system creates. I have upgraded a couple of systems and my feeling is that i saw more available space under 7.3.
Iam also wondering when your disks have only 50% or so allocated if the distributed spare only reserved this 50% for example.
I have a technical whitepaper in mind but i have to check my docs.
Regards
Joerg
DELL-Bob Mi
230 Posts
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April 24th, 2019 11:00
Refer to: Dell EMC SC Series Distributed Spare
https://downloads.dell.com/manuals/all-products/esuprt_software/esuprt_it_ops_datcentr_mgmt/general-solution-resources_white-papers5_en-us.pdf
On page 7 of this document it states: 'The total number of drives and the amount of usable space in the array does not change; the only change occurs in the layout of the spare, or reserve space.' This is because now in place of having hot spares you have spare Raid Extents available for disk failures
Here is a link to all Dell Storage Center OS 7.3 technical publications
https://www.dell.com/support/article/us/en/04/sln312416/dell-storage-center-os-73-technical-publications?lang=en
5X5CX62
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April 24th, 2019 15:00
Thanks for the answer.
How much would the new strategy reduce rebuild time on 7.2k drives?
Is it advisable to switch to this feature for existing SCv2000 and SCv2080 after upgrading to SCOS 7.3?
DELL-Bob Mi
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April 26th, 2019 14:00
This will decrease the amount of time it takes to rebuild a disk by approximately 100% to 200% so it should take at least half as much time to rebuild a failed disk depending upon how many disks are in use. The more disks the faster they will rebuild. Page 13 of the guide shows how the rebuilds are reduced.