I have some 18TB Seagate Disks on a DL380 Gen8 HP server with p420i raid controller, with 2GB cache module. I have created a RAID5 with 16TB disks but with 18TB disks, all disks are recognized but when I want to create a RAID volume, all disks fail. (a pic enclosed)

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I did not find any HP document that help me find out what is the max disk size a p420i can support in practice. I know that HP indicated that only 8TB disk is officially supported but I have tested 16TB disks and it works well.

In general, how can I be sure if a raid controller can support a specific disk size in practice? Theoretically, what is the problem with a disk model that causes raid creation failure?

  • 1
    That's what happens when you don't update firmware for 10 years. You're going to miss a few things, like support for larger capacity devices/volumes. Also I suspect your "works well" didn't really test anything like how long it takes to resync a failed array with 30 TB of data. On non-performant hardware.
    – Greg Askew
    Nov 13, 2022 at 19:12
  • Try to upgrade both the controller and the server firmwares
    – shodanshok
    Nov 14, 2022 at 10:52

3 Answers 3


I Can Confirm that 20TB Seagate Exos X20 Drives will work on the P420 Controller Pic of working Raid 1 Setup with 2x 20TB HDDs

The Creation Wizards Page in Raid BIOS

  • You are right. Actually my disks were EXOS X18z which could not be used without their special driver, so they couldn't be used in raid controller (I don't know what are these type of disks, they only work with their driver on Linux). Thanks anyway.
    – raitech
    Feb 11 at 9:23

Consider yourself lucky you came here at this stage, and that this didn't work.

Firstly you're not supposed to run non-HPE disks on HPE disk controllers, I know some work but we've had a lot of people come here since serverfault started who have lost data by doing what you're trying to do.

Secondly - friends don't let friends use RAID 5 - not at all - not for well over a decade - and certainly not on such large disks - it's staggeringly dangerous for your data and, you guessed it, we get a LOT of people come here asking us to help recover their data because they used R5. It's really frowned upon and I couldn't stand by and let you risk your data like this - R1/10, R6/60 and ZRAID are really the only games in town, and the only ones trusted by professional sysadmins and storage admins.

So to recap, don't do this with the p420i and don't use R5 - pick up any old third-party RAID controller and use R6 instead please - anything else and we'll be seeing a much more stressed version of you here in the future.

  • Absolutely right. The question is how can I find a raid controller that supports it and why a controller can't work with a large disk theoretically.
    – raitech
    Nov 14, 2022 at 4:26
  • Hope by ZRAID you mean RAIDZ2 because AFAIK RAIDZ is equivalent of RAID5. Nov 14, 2022 at 10:59
  • 1
    @RomeoNinov - yes of course, thank you, I don't deal with RAIDZ on a daily basis so it's easy for me to make commissions like that!
    – Chopper3
    Nov 14, 2022 at 11:44

Try to work with period-correct equipment.

Gen8 HPE hardware is circa 2012-2015... So 10 year-old technology at this point.

18TB disks showed up around 2019/2020.

You should focus on using more current server equipment.


Because the gear you're working with was not designed to be forward-compatible.
Firmware, support, updates, etc. are not available on end-of-life equipment, so a new installation with recent disks is not guaranteed to work.

  • Right. Even recent raid controllers do not state any max disk size. So I have to test all to find one.
    – raitech
    Nov 14, 2022 at 4:30
  • @raitech That's the wrong takeaway from my comment.
    – ewwhite
    Nov 14, 2022 at 8:24

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