You can backup the root filesystem to a file using "ufsdump 0uf /path-to-file /dev/rdsk/c0t0d0s0" after going to single user mode. You can use that file to restore the UFS root file system in case of HDD outage.
Ok, but if I loose the output of ufsdump command I will loose the backup copy as well... I can put it on another server, but how to restore it
Of course you need to put the dump in another server as in case of outage you will loose the backup too. You can put it to a removable media but I am not 100% sure if the ufsrestore will work when you restore the root UFS as you have to boot from Solaris 10 DVD in single-user mode and mount it to access the dump.
You may check also this thread:
It seems that it is possible to mount the USB drive when in single user mode. Hope it helps.
Moderator Comment and Action:
You cross-posted this same inquiry to at least one other forum web site:
... and failed to mention that fact.
Good forum etiquette would have you at least paste a URL to your other post(s) so that people wouldn't waste their time posting a reply that is the same as what you've been told elsewhere. That same forum etiquette of a pasted link also gives people the opportunity to (perhaps) learn from the responses you might get on the other forum web site.
Poor etiquette gets posts locked.