questions about sas/sata hdd speeds

[ari2asem]

maybe i am asking stupid question. but yet want to ask it

this spec-sheet is just a example

https://toshiba.semicon-storage.com...product-manual/eHDD-MG08-Product-Overview.pdf

for both sata3 and sas3 i see the same MAX.SUSTAINED TRANSFER SPEED = 262 Mb/s

my question is only about the speed, not about other advantages of sas3 over sata3 when using enterprise class hdd's (like seagate exos x-serie, wd ultrastar hc-serie)

1.) why should we use SAS3 drives when they have the same max.speed as SATA-3?​

2.) or does it matter (speed-wise) when sas3-drives are part of zfs-pool? for example, when rebuilding the pool (or vdev) after replacing failed hdd​

​

once again, i am sorry for my stupid question

 

[Rand__]

if you exclude all other criteria and purely limit yourself to max speed then it does not matter which you run - the drive cannot provide data faster then max speed only due to another interface and both SATA and SAS3 far exceed that max speed.

But as you already correctly said - there is more to SAS than speed...

 

[i386]

Sas drives (10 or 15k rpm) are faster than sata drives.
The drive you linked is a nearline sas drive (sata drive mechanics/motors + sas interface).

 

[gea]

You are limited by disk performance not interface performance.

The only possible performance advantage of SAS is when you go above say 500 MB/s disk performance (6G Sata) as there is 12G SAS. If the disks are even faster than 12G like the WD SS530, you can use 2 x 12G dualpath SAS.

The main advantage of SAS is a much robuster data transfer with up to 10m cable length (Sata 1m) and all the expander and multipath options.

Another advantage of SAS is full duplex (Sata half duplex) data transfer. This is important in a multi user environment with concurrent read/write.