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Disk mirroring (ASR9000, CRS)



Disk mirroring as described in IOS XR Fundamentals:

"At the time of writing this book, disk mirroring is supported only between disk0: and disk1: on both CRS-1 and c12000 platforms. Disk mirroring works by replicating critical data from the primary boot device onto another storage device on the same RP. This other storage device can be referred to as a
mirrored disk or simply as a secondary device. If the primary boot device fails, applications continue to be serviced transparently by the secondary device, thereby avoiding a switchover to the standby RP. The failed primary storage device can be replaced or repaired without disruption of service."

By now, disk mirroring is also supported on ASR9000 platform:


Sam and Xander have commented that disk mirroring on ASR9000 doesn't make much sense as the disk themselves are not field replaceable.

For example: if RSP0/disk0 goes faulty, RSP0/disk1 takes over and a RSP switchover was prevented. Nonetheless, we will have to replace RSP0/disk0 eventually, so all we did with disk mirroring is postpone the maintenance action. Or am I missing something?

What about the CRS platform? Is the situation there the same or are disks field repleacable?


Thank you and kind regards,


11 Replies 11

Cisco Employee
Cisco Employee

the usb disks are soldered on the board, they are not components that we can take out from the RP.

if the disk fails, an RMA is necessary (board replacement), due to the high density of components on a board it is becoming harder and harder to manually/field replace parts unfortunately.

the disk mirroring was something historically inherited hence it being there, but realistically it doesnt make much sense anymore today.

to maintain similarity between devices, disk partitioning was done, but having a disk0 and disk1 on the same phy chip doing mirroring makes no sense :)



Hi Xander,


Thank you for your prompt answer.

Can the documentation be updated to reflect the information you provided?


Kind regards, Karlo.