Copy-back and copy-back-less operation

After the failed dis kas been replaced with a new disk, data on the hot-spare disk is retrieved (copied back) to the new disk. The copy-back function restores the RAID group while maintaining redundancy after the rebuild has been performed for the hot-spare in the RAID group.

copy-back figure

Copy-back-less function is a feature which builds hot-spare disks into a RAID configuration after the completion of rebuild or redundant copy and the internal RAID configuration of the failed disk is changed to hot-spare disk. Immediately after maintenance and replacement, it can start working as a hot-spare disk. This feature means that the copy-back process is no longer required.
Note: Copy-back-less function is featured by ETERNUS AF and ETERNUS DX S3 or later, only.

copy-back-less figure

Rebuild: 4 hours, copy-back: 4 hours, disk replacement: 0.5 hours

Working time for replacement of diskTime until HS becomes available
Copy-backMax 8.5 hours
(Rebuild + Replacing Disk + Copyback)
8.5 hours
(Rebuild + Replacing Disk + Copyback)
Copy-back-lessMax 4.5 hours
(Rebuild + Replacing Disk)
4.5 hours
(Rebuild + Replacing Disk)

The administrator can choose between copy-back and copy-back-less operation via the GUI. (Only for ETERNUS AF and ETERNUS DX S3 or later.)


  • Disk replacement time is drastically reduced
  • RAID availability is improved as the hot-spare dontime is reduced
  • I/O performance degradation during the copy-back process can be avoided

Product Requirements

Supported StoragesAll-Flash ArraysETERNUS AF150 S3
ETERNUS AF250 S3/S2, AF250
ETERNUS AF650 S3/S2, AF650
Hybrid Storage SystemsETERNUS DX60 S5/S4/S3
ETERNUS DX100 S5/S4/S3, DX200 S5/S4/S3
ETERNUS DX500 S5/S4/S3, DX600 S5/S4/S3
ETERNUS DX8700 S3/S2, DX8900 S4/S3
ETERNUS DX60 S2, DX80 S2, DX90 S2
ETERNUS DX400 S2 series

Further Information

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