how can I sync 2 almost identical disk after dd

Question

Lets say I have /dev/sda and /dev/sdb.
Before, I run dd if=/dev/sda of=/dev/sdb bs=128M, and it succeeded.

Then after some time, there is update on first disk, and I want to clone it to second disk. But I don't want to run dd from beginning, because ... well it takes time.
Any solution to update on the /dev/sdb without dd'ing from start?

UPDATE : the disk actually is ntfs, so rsync is not a solution. Also, I want the second disk to be bootable like the source disk, using rsync would break so many things.

How can you know which blocks are updated? What is the reason for this? — Michael Hampton, May 28 '19 at 06:45
@MichaelHampton I'm trying to clone server to server over ssh, but I don't want to shutdown the old server just for dd'ing 1TB data over 100mbps connection. — Rinaldo Jonathan, May 28 '19 at 06:46

score 1 · Answer 1 · answered May 28 '19 at 06:46

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I bet RSync will do the job perfectly. Actually, you could also have used it to clone your disks at first instead of using dd.

answered May 28 '19 at 06:46

Httqm

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the disk is ntfs. but I want solution to be as general as possible. and I want the destination disk to be bootable like the source disk, and using rsync would make different uuid, broken bootloader and things like that. – Rinaldo Jonathan May 28 '19 at 06:47
@RinaldoJonathan Got it ;-) You should have said this (and other details you gave in other comments) while asking your question. Can you, please, update your initial question with these constraints ? – Httqm May 28 '19 at 06:50
okay, will do. /15char – Rinaldo Jonathan May 28 '19 at 06:51

score 1 · Accepted Answer · answered May 28 '19 at 07:00

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You can try using blocksync, bdsync or even rsync --inplace --copy-device (if your rsync version supports it) to achieve what you ask.

Be aware that all these methods will read the entire source and destination drives, but they will transfer only changed blocks.

answered May 28 '19 at 07:00

shodanshok

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I never know that there is rsync with --copy-device. Thanks! – Rinaldo Jonathan May 28 '19 at 07:01
I was thinking of a more complex solution. Good thing this works. – Overmind May 28 '19 at 07:11

how can I sync 2 almost identical disk after dd

2 Answers2