Re: how to know a hard drive will mix well

On 02/02/2023 12:43, David T-G wrote:

Hi, all --

I have

   diskfarm:~ # mdadm -D /dev/md51 | egrep /dev/
   /dev/md51:
	 0     259        9        0      active sync   /dev/sdb51
	 1     259        2        1      active sync   /dev/sdc51
	 3     259       16        2      active sync   /dev/sdd51
	 4     259       23        3      active sync   /dev/sdj51

Toshiba X300 10T

   diskfarm:~ # smartctl -i /dev/sdb | egrep '(Model|Number|Version):'
   Device Model:     TOSHIBA HDWR11A
   Serial Number:    61U0A0HQFBKG
   Firmware Version: 0603

drives in my disk farm, and it's about time to grow again.  As I
shopped around, I stumbled over a WD Red Plus 12T WD120EFBX drive at
just $10 more, and who wouldn't want an extra 2T for ten bucks?  So I'm
contemplating rolling in a different model.  But how do I know that it
will fit well into the mix?

The X300 is a 7200rpm 256Mcache 6G/sec CMR drive.  The Red Plus is also
listed as a 7200rpm* 256Mcache 6G/sec CMR drive.  They certainly sound
equivalent.  What else do I need to consider, and where else do I need
to look to learn?

I don't trust WD. That said, a lot of people do. I've got two 4TB 
Ironwolves, one 3TB Barracuda (slap wrist!), and one 8TB X300.

So mixing drives isn't a problem - just take a look at the Ironwolf - 
that might give you extra capacity too.

* The spec actually says "7200 RPM Class".  Does that mean not really
7200rpm?  That wouldn't surprise me in this modern day and age, and if
the X300 also isn't really then that also wouldn't.

Drives now are "Constant Head Speed" not constant rpm. I'm guessing, 
that what it means is that for the inner tracks it spins at 7200, and as 
the heads move out, the rpms slow down to keep the speed the head is 
going over the platter constant.

Cheers,
Wol