SSDs for Pegasus1 R4

  • Last Post 25 March 2022
John Moss posted this 24 March 2022

I have a Pegasus R4 attatched to a 2012 Mac Mini. It currently has four 3.5" 1TB Seagate HDD in it. It's configured as RAID 5.

I'd like to start switching the HDDs out for SSDs, to improve speed and reduce heat and noise.

(1) Can I do it one at a time? Will the Pegasus be able to manage a mix of HDD and SSD drives?

(2) Can I use any SATA 2.5" SSD drives? Or are there some specific things I need to look for?

I was basically looking at one of these choices:

Samsung 870 EVO SATA III SSD 1TB 2.5” 


Crucial MX500 1TB 3D NAND SATA 2.5 Inch Internal SSD, up to 560MB/s


Western Digital 1TB WD Green - SATA III 6 Gb/s, 2.5/7mm, Up to 545 MB/s


Western Digital 1TB WD Blue 3D NAND - SATA III 6 Gb/s, 2.5"/7mm, Up to 560 MB/s

OWC Mercury Electra 3G 2.5-inch Serial-ATA 7mm SSD


OWC Mercury Electra 6G 2.5-inch Serial-ATA 7mm SSD




R P posted this 25 March 2022

Hi John,

Sorry, you can't mix SSDs and HDDs in an array. If you replace a spinning drive with an SSD you won't be able to rebuild to it.

While we can't endorse any particular SSD, one thing to keep in mind is that there are several types of TRIM.

  • Non-deterministic TRIM: Each read command to the logical block address (LBA) after a TRIM may return different data.
  • Deterministic TRIM (DRAT): All read commands to the LBA after a TRIM shall return the same data, or become determinate.
  • Deterministic Read Zero after TRIM (RZAT): All read commands to the LBA after a TRIM shall return zero.

SSDs with different TRIM types can't be mixed in an array. This should not be a problem if you use (4) of the same model drive.