Not sure what kind of server you are referring to but our servers can take SAS and SATA at the same time. We build plenty of servers running FreeBSD which in some cases have SATA SSD for boot drives (in a RAID-1) and then X amount of either SATA or SAS or both in a different RAID configuration all connected to the same high quality RAID Controller.

I have yet to see any complaint with the configurations we've done for our clients.


SAS drives can be much faster. 15K RPM vs. SATA 7.2K. Your choices would depend on how busy the server is.

Regards,
Lanny

On 8/9/2017 11:29 AM, Josh Paetzel wrote:


On Wed, Aug 9, 2017, at 09:55 AM, Frank Leonhardt (m) wrote:
Simple answer is to use either. You're running FreeBSD with ZFS, right?
BSD will hot plug anything. I suspect 'hot plug' relates to Microsoft
workaround hardware RAID.

Hot plug enclosures will also let the host know a drive has been pulled.
Otherwise ZFS won't know whether it was pulled or is unresponsive due to
it being on fire or something. With 8 drives in your array you can
probably figure this out yourself.

SAS drives use SCSI commands, which are supposedly better than SATA
commands. Electrically they are the same. SAS drives are more expensive
and tend to be higher spec mechanically, but not always so. Incidentally,
nearline SAS is a cheaper SATA drive that understands SAS protocol and
has dual ports. Marketing.

Basically, if you really want speed at all costs go for SAS. If you want
best capacity for your money, go SATA. If in doubt, go for SATA. If you
don't know you need SAS for some reason, you probably don't.

Regards, Frank.


On 9 August 2017 15:27:37 BST, "Mikhail T." <m...@aldan.algebra.com>
wrote:
My server has 8 "hot-plug" slots, that can accept both SATA and SAS
drives. SATA ones tend to be cheaper for the same features (like
cache-sizes), what am I getting for the extra money spent on SAS?

Asking specifically about the protocol differences... It would seem,
for example, SATA can not be as easily hot-plugged, but with
camcontrol(8) that should not be a problem, right? What else? Thank
you!
--

I have a different take on this.  For starters SAS and SATA aren't
electrically compatible.  There's a reason SAS drives are keyed so you
can't plug them in to a SATA controller.  It keeps the magic smoke
inside the drive.  SAS controllers can tunnel SATA (They confusingly
call this STP (Not Spanning Tree Protocol, but SATA Tunneling Protocol)
It's imperfect but good enough for 8 drives.  You really do not want to
put 60 SATA drives in a SAS JBOD)

SAS can be a shared fabric, which means a group of drives are like a
room full of people having a conversation.  If someone starts screaming
and spurting blood it can disrupt the conversations of everyone in the
room.  Modern RAID controllers are pretty good at disconnecting drives
that are not working properly but not completely dead.  Modern HBAs not
so much.  If your controller is an HBA trying to keep a SAS fabric
stable with SATA drives can be more problematic than if you use SAS
drives...and as Frank pointed out nearline SAS drives are essentially
SATA drives with a SAS interface (and are typically under a $20 premium)

If performance was an issue we'd be talking about SSDs.  While SAS
drives do have a performance advantage over SATA in
multiuser/multiapplication environments (they have a superior queuing
implementation) it's not worth considering when the real solution is
SSDs.

My recommendation is if you have SAS expanders and an HBA use SAS
drives.  If you have direct wired SAS or a RAID controller you can use
either SAS or SATA.  If your application demands performance or
concurrency get a couple SSDs.  They'll smoke anything any spinning
drive can do.

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