Where did my second external hdd go?

Hello,
I just mounted two external hard drives on my raspberry pi. But one HDD seems gone suddenly.

If I run these following commands I get an output like there are two HDDs.

sudo blkid
/dev/mmcblk0p1: LABEL_FATBOOT="boot" LABEL="boot" UUID="6341-C9E5" TYPE="vfat" PARTUUID="ea7d04d6-01"
/dev/mmcblk0p2: LABEL="rootfs" UUID="80571af6-21c9-48a0-9df5-cffb60cf79af" TYPE="ext4" PARTUUID="ea7d04d6-02"
/dev/sda1: UUID="465a1ae0-2d11-4499-824f-d1a97b8ce866" TYPE="ext4" PARTUUID="30c24214-01"
/dev/sdb1: LABEL="samsung_320" UUID="0835bf91-2191-483c-92bc-96952942ed46" TYPE="ext4" PARTUUID="9d84ca5f-c200-4f52-a4c2-ccaff1bf54e9"
/dev/mmcblk0: PTUUID="ea7d04d6" PTTYPE="dos"

lsusb
Bus 002 Device 004: ID 152d:0578 JMicron Technology Corp. / JMicron USA Technology Corp. JMS567 SATA 6Gb/s bridge
Bus 002 Device 002: ID 152d:0578 JMicron Technology Corp. / JMicron USA Technology Corp. JMS567 SATA 6Gb/s bridge
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 002: ID 2109:3431 VIA Labs, Inc. Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

Before (a hour ago) I mounted them like:

sudo mkdir /mnt/seagate_320
sudo mkdir /mnt/samsung_320

sudo mount /dev/sda1 /mnt/seagate_320
sudo mount /dev/sdb1 /mnt/samsung_320

Too make them mounted after a reboot I added this to my fstab:
proc            /proc          proc    defaults          0      0
PARTUUID=ea7d04d6-01  /boot          vfat    defaults          0      2
PARTUUID=ea7d04d6-02  /              ext4    defaults,noatime  0      1
PARTUUID=30c24214-01  /mnt/seagate_320 ext4  defaults,auto,users,rw,nofail 0 0
PARTUUID=9d84ca5f-c200-4f52-a4c2-ccaff1bf54e9  /mnt/samsung_320 ext4  defaults,auto,users,rw,nofail 0 0
# a swapfile is not a swap partition, no line here
#  use  dphys-swapfile swap[on|off]  for that

First I restarted the raspberry pi and I am pretty sure I could ssh to both HDDs, but now an hour later I can just see the seagate_320. No trace of the samsung_320??
Right now I transfer a lot of files to the seagate_320. But even that I thought there would be no problem seeing the samsung_320.

What do you think might have gone wrong?

Best regards
Fredrik