I would wait ... an "identical" drive would be a certified drive for this controller and you would eliminate the chances of firmware incompatibilities.  I would especially recommend this if the server hosts critical data/services.  Introducing a non-certified drive (although an enterprise-class drive) could cause unpredictable issues down the road. Most drive update utilities are bootable, so a restart would be necessary.  The PERC firmware also requires a reboot, and should be done while the array is healthy (after it rebuilds).  Be sure to update your LifeCycle Controller/iDRAC and BIOS before updating the PERC.
PE T605 with Perc 6/I three drives, Raid 5. One drive has failed, they are Seagate 250gb SATA 7200rpm drives. I could order one of these drives and wait a day or two or can get a different capacity/brand today and replace it tonight. The replacement is a Western Digital 1TB 7200rpm "enterprise" drive. I just want to verify that this will work, I realize it will only use 250gb of the 1TB so I'm losing that capacity but are there any other specs I need to look for or verify? or is it best to wait for an identical drive? Also, the existing drives apparently need a firmware update re: [URL] this indicates that the MA07 needs to be upgraded to MA08. There is no MA08 just MA10 so I will install that. I've not done a firmware update on a drive, will this require a restart of the server? The controller firmware is also out of date, same question with this will it require a server restart? I plan to do the firmware upgrade after the replacement drive is installed and the array is rebuilt and a backup run, that seems the most prudent plan, or is it better to do the firmware upgrades first? Thanks!  
T605 Perc 6/I failed drive, replace with different capacity/brand