Entrei em contato com o suporte técnico da Crucial e recebi a seguinte resposta: (8 horas depois)
Thank you for contacting us. The behavior you are describing is
consistent with TRIM commands not executing on the drive (which may
result from lots of writing and rewriting, especially OS installs, not
done on the OS level). The accumulation of 'junk' data from file
deletions, even reformats, basically clogs up the drive and reduces or
sometimes even halts performance and can even dismount the drive. A
secondary feature called Garbage Collection activates when the drive
is powered, but has no data throughput, for an extended period, and
does background cleanup on our SSDs which can make up for the lack of
TRIM.
If this is the cause of your drive's behavior, a period of idling the
drive without any data being written or read actively will improve its
performance. We recommend you perform this idle period on a desktop
computer because it allows you to only connect the SATA power
connection. However, a USB enclosure with an external power source
will also work. A laptop computer will also work, but you’ll have to
connect the drive and navigate to the systems BIOS menu. (Please refer
to your system manufacturer’s documentation on how to access the
BIOS.)
For laptops, we don’t recommended using a USB enclosure powered via
USB; dedicated AC power is preferable. In addition, Apple users must
hold the Option key while they power on the system (with the SSD
installed). This will boot the Mac to the Startup Manager screen. The
Startup Manager screen works like the BIOS screen on a laptop, in that
it gives the drive power without any data throughput. An alternative
Apple method is to close all open programs (including background
processes) after startup and idle on your desktop. Just power the
drive and let it sit, preferably overnight, but even a few hours
should improve performance if this is the cause of your drive's
erratic performance, though full Garbage Collection takes 8-24 hours
and should be resumed when you can be without that system for an
extended period.
Este não foi o problema ( resposta de rob resolveu o problema imediatamente), mas pode ajudar alguém.
Eu estava usando o controlador RAID x79 da Intel, que envia comandos TRIM, então não acho que isso seja aplicável a mim.