The XPS13 9300 ships with BIOS in Raid ON-mode for SSD-conf. What are the reasons for this? I know RAID as a way to increase reliability and/or performance on a multi disk platform. Why is it default on a single disk machine? Pros/cons in switching to AHCI?
(If it matters, my 9300 is equipped with an M.2 NVMe 2TB disk.)
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@TommyW_SE Short version: If you're about to clean install an OS, switch to AHCI. RAID mode offers no benefit on an XPS 13 that only supports a single SSD. If you're curious about why it's there, read on.
Long version:
RAID mode seems to be the default on most if not all Dell laptops and desktops that support it, except for the handful of systems that Dell offers with Linux pre-installed from the factory. I suspect Dell does it these days simply to standardize their builds a bit and also because it doesn't have any downsides for them, but it can have some downsides for users.
RAID mode activates the Intel Rapid Storage controller, which abstracts the storage from the OS and allows certain other features to be used. Back in the Windows 7 days, that abstraction meant that RAID mode could be used to allow Windows 7 to be installed onto NVMe SSDs. Windows 7 didn't have native support for NVMe, but with RAID mode, the OS just needs the Intel Rapid Storage driver and then it doesn't matter to the OS that the storage "behind" that controller is NVMe. By comparison, AHCI mode exposes the storage directly to the OS, which means the OS needs to have native support for the storage device's data interface, i.e. NVMe in this case.
But RAID mode is also required for using certain other features, such as Intel Rapid Start, Intel Smart Response, and more recently Intel Optane. But the first two are only used when you're pairing a spinning hard drive with a small SSD cache, and Optane is only used with actual Optane devices.
In terms of downsides:
So again, for Dell I guess it makes sense to just use RAID mode everywhere for consistency, since they of course do sell some systems with Optane (and Smart Response and Rapid Start in the past), as well as other systems that actually do have multiple disks and therefore support actual RAID setups. And the downsides don't really matter to them.
But for individual users performing a clean install, switching to AHCI means you don't have to worry about providing an Intel RST driver, you can use Linux if desired, and you can use a vendor-provided NVMe driver if desired (and available).
However, this setting is only really meant to be changed before reinstalling an OS. If you want to switch WITHOUT doing that, you'll render your OS unbootable until you switch back. Apparently it's possible to work around this by booting into Safe Mode ONCE after making the switch, which will allow Windows to start and reconfigure itself. After that, you should be able to boot normally. But if you don't need any of the benefits of AHCI mode, you're not really losing anything by sticking with RAID.
@TommyW_SE Short version: If you're about to clean install an OS, switch to AHCI. RAID mode offers no benefit on an XPS 13 that only supports a single SSD. If you're curious about why it's there, read on.
Long version:
RAID mode seems to be the default on most if not all Dell laptops and desktops that support it, except for the handful of systems that Dell offers with Linux pre-installed from the factory. I suspect Dell does it these days simply to standardize their builds a bit and also because it doesn't have any downsides for them, but it can have some downsides for users.
RAID mode activates the Intel Rapid Storage controller, which abstracts the storage from the OS and allows certain other features to be used. Back in the Windows 7 days, that abstraction meant that RAID mode could be used to allow Windows 7 to be installed onto NVMe SSDs. Windows 7 didn't have native support for NVMe, but with RAID mode, the OS just needs the Intel Rapid Storage driver and then it doesn't matter to the OS that the storage "behind" that controller is NVMe. By comparison, AHCI mode exposes the storage directly to the OS, which means the OS needs to have native support for the storage device's data interface, i.e. NVMe in this case.
But RAID mode is also required for using certain other features, such as Intel Rapid Start, Intel Smart Response, and more recently Intel Optane. But the first two are only used when you're pairing a spinning hard drive with a small SSD cache, and Optane is only used with actual Optane devices.
In terms of downsides:
So again, for Dell I guess it makes sense to just use RAID mode everywhere for consistency, since they of course do sell some systems with Optane (and Smart Response and Rapid Start in the past), as well as other systems that actually do have multiple disks and therefore support actual RAID setups. And the downsides don't really matter to them.
But for individual users performing a clean install, switching to AHCI means you don't have to worry about providing an Intel RST driver, you can use Linux if desired, and you can use a vendor-provided NVMe driver if desired (and available).
However, this setting is only really meant to be changed before reinstalling an OS. If you want to switch WITHOUT doing that, you'll render your OS unbootable until you switch back. Apparently it's possible to work around this by booting into Safe Mode ONCE after making the switch, which will allow Windows to start and reconfigure itself. After that, you should be able to boot normally. But if you don't need any of the benefits of AHCI mode, you're not really losing anything by sticking with RAID.
This setting is only really meant to be changed before reinstalling an OS.
Switching to AHCI means you don't have to worry about providing an Intel RST driver,
... And the downsides don't really matter to Dell.
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Good summary.
Thank you @jphughan, a great answer!
I believe there are some XPS 9300s out there which come with the Intel 660p QLC drive with Optane memory, particularly those with the 512GB configuration. I'm guessing these systems will still need to have RAID on?
@describee From what I remember reading from others here, if Optane SSDs are used in AHCI, they work just like regular SSDs and Optane acceleration can't be enabled. So if Dell is selling XPS 13s with Optane drives, then yes they would need to stay in RAID mode. But at least on other Dell systems where I've seen Optane offered, the storage option on the system specifically mentions Optane. But maybe that's changing?
Perhaps so. For what it's worth I found that I had the Intel Optane software installed on my 9300 by default even though I didn't have an Optane drive.
@describee It's part of the Rapid Storage Technology application. Even that doesn't offer much functionality when running a single SSD, but again I suspect this is a case of factory standardization even in situations where the result is not a ideal for individual cases as it could be.
On My Mobile Precision 7740 and 7750, I could not run 2 TB SSDs in RAID mode. I had to switch to AHCI for them to pass diagnostics.
Are there any performance differences between those two modes?