Several weeks ago Samsung has released a fix for the 840 series of their SSDs that had performance issues on long time stored data. While the fix procedure is quite simple to apply on Windows, when you use your SSD on a GNU/Linux powered system it can be quite tricky. So to fix your SSD you will need a bootable USB key with the Samsung binaries. Moreover the Samsung documentation is not really well written and can lead to confusion. So here are the steps to fix dear GNU/Linux users' SSDs.
Firstly, prepare a USB key (at least 512 MB, just to be sure) and download FreeDOS.
Creating the bootable USB key
Once FreeDOS is on your computer, plug the USB key in and find the device to interact with it. You can generally find the device using the dmesg command. This will output something like this:
[1017607.068095] usb 2-1: new high-speed USB device number 110 using ehci-pci
[1017607.278127] usb 2-1: New USB device found, idVendor=1b1c, idProduct=1ab1
[1017607.278135] usb 2-1: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[1017607.278140] usb 2-1: Product: Voyager
[1017607.278145] usb 2-1: Manufacturer: Corsair
[1017607.278150] usb 2-1: SerialNumber: AA00000000000634
[1017607.278936] usb-storage 2-1:1.0: USB Mass Storage device detected
[1017607.279084] scsi12 : usb-storage 2-1:1.0
[1017608.389828] scsi 12:0:0:0: Direct-Access Corsair Voyager 1100 PQ: 0 ANSI: 0 CCS
[1017608.390448] sd 12:0:0:0: Attached scsi generic sg2 type 0
[1017608.391272] sd 12:0:0:0: [sdb] 15663104 512-byte logical blocks: (8.01 GB/7.46 GiB)
[1017608.392259] sd 12:0:0:0: [sdb] Write Protect is off
[1017608.392266] sd 12:0:0:0: [sdb] Mode Sense: 43 00 00 00
[1017608.394784] sd 12:0:0:0: [sdb] No Caching mode page found
[1017608.394792] sd 12:0:0:0: [sdb] Assuming drive cache: write through
[1017608.402247] sdb: sdb1
[1017608.405637] sd 12:0:0:0: [sdb] Attached SCSI removable disk
In this case you want to use the /dev/sdb dive as seen in the log.
Now you can just write the FreeDOS image on the USB disk. The image is compressed so you'll need to decompress it before.
$ bunzip2 FreeDOS-1.1-memstick-2-256M.img.bz2
$ dd if=FreeDOS-1.1-memstick-2-256MB.img of=/dev/sdb bs=512k
Copying the Samsung binaries
Download the Samsung binaries.
Mount the USB key and unzip those binaries at the USB key root. In this way you will be able to use them from FreeDOS later.
# mount /dev/sdb1 /mnt
# unzip Samsung_Performance_Restoration_USB_Bootable.zip
# mv 840Perf/* /mnt
# umount /mnt
# eject /dev/sdb
Plug the USB key in your machine and reboot the host. Do what is necessary to boot on the USB key. Choose the option 4 of FreeDOS "Load FreeDOS without driver".
Once FreeDOS is running just run the PERF.EXE file and the Samsung tool will start. Enter the index in front of the SSD you want to upgrade and fix. The utility will take care of everything (firmware upgrade and fix). Note that the pass to fix the SSD can take some time.
Once the tool has finished to fix your SSD just reboot the host by typing reboot in FreeDOS. Do not forget to unplug the USB key to avoid booting from it later.