--Due to some Hardware problem SAN drive having LDF files for all of the system database lost.
--Now you have recreated a new drive with same drive letter but contents are not there.
--You have database backup for all the system databases and other user databases.
--You have MDF file for system database as well.
1) first use rebuildm utility .If that fails then ,
2) Restore all SYSTEM databases on a test instance of SQL with “new” as prefix.( remember you have backups :D )
--Detach those databases from the test instance.
--On original instance of SQL rename all the previous system MDF files with “old” as prefix.
--Copied all the MDF & LDF files from test instance to this actual instance folder and rename data file named to actual one (like master.mdf, model.mdf, msdbdata.mdf).and log files as well .
--Gave proper permissions to all of the newly copied files if needed .
--Start SQL server and it starts successfully.
--Attach all user database and everything will work fine.
Hope it helps :)