How to ZFS on Dual-Actuator Mach2 drives from Seagate without Worry

John-S · July 30, 2023, 2:56pm

Howdy folks, now that I’ve ordered for my own needs I wanted to share that Newegg has refurb SATA Exos 2x18TB “Refurb” drives available for $219 each.

The SAS version is a bit easier to configure as each actuator is presented as a unique LUN. The SATA version presents a linear block address range where the “split” between actuators is precisely at MAX_LBA/2. Even though I have to create two properly aligned GPT portions while accounting for GPT partition overhead, I find the SATA versions to be far more versatile and performant while negating the need for complicated/expensive 12G SAS topologies and HBAs.

The precise “magic” to get the provisioning right is here:

github.com

suykerbuyk/disk-helpers-scripts/blob/d1c58af8fe445a7adb2dd351468aecbe4acab6da/exosx2_zfs_ops.sh#L362


      
          		then
                          	run "zpool labelclear -f ${LUN}-part1 &>/dev/null || true " &
          		fi
          	done
          	wait
          	printf "END: $TGT ${FUNCNAME[0]}\n"
          }
          
          
#=======================================================
          # Creates GPT partitions aligned to Osprey LBA splits
          CreateOspreyPartitioning(){
          	printf "RUN: $TGT ${FUNCNAME[0]}\n"
          	ALIGN=$((1024*4))
          	GPT_OVERHEAD=34
          	for LUN in ${TARGET_LUNS[*]}
          	do
          		SERIAL=$(echo ${LUN} | awk -F '_' '{print $2}')
          		LARGEST_END="$(sgdisk -a ${ALIGN} -E ${LUN} | grep -v Creating)"
          		LARGEST_BEG="$(sgdisk -a ${ALIGN} -F ${LUN} | grep -v Creating)"
          		TOTAL_SECTORS=$((GPT_OVERHEAD + LARGEST_END))
          		MID_LBA=$((TOTAL_SECTORS/2))

That script also happens to be a relatively complete TUI for prepping SATA DA drives for ZFS.

In other news, I’ve a 45 drives chassis on the way, hope to add some modules to “Huston/Cockpit” to provision SATA dual actuator drives.