Re: SSD not seen by CrystalDiskInfo
Juyst received an xps 13 i purchased off outlet. getting 1200mb/s seq read and 450 seq/write! Checked bios and noticed SATA is set to RAID for some reason. It should be AHCI right?
Slow write performance on Toshiba NVMe SSDs in the Inspiron 7577 (and other systems, including non-Dell systems) has been discussed quite a bit both on this forum and elsewhere on the Internet. There's no good answer other than replacing it with a Samsung unit, unfortunately. Dell doesn't seem to accept this as grounds for a warranty claim, and even if they did, there would be no guarantee that the replacement wouldn't be another Toshiba SSD. Obviously not an ideal situation especially when some other Inspiron 7577s ship with Samsung SSDs that perform as expected, so it's a bit "luck of the draw", but that's where things stand at the moment.
As for RAID vs. AHCI, it doesn't make a difference in your case. All Dell systems ship in RAID mode mostly for historical reasons. RAID mode is required to allow Windows 7 to run on an NVMe SSD (although new systems won't run Windows 7 properly for other reasons), and it's also used for systems that have a spinning hard drive and a small SSD cache module so that the latter can accelerate the performance of the former. If neither of those things applies to you, then you can switch to AHCI, but your performance won't change meaningfully in either direction, and making that change while you have an OS installed as opposed to doing it before performing a clean install involves some extra steps anyway, so it's not really worth it.