How to use XFS on a Synology NAS device

After returning from a trip to Israel and Jordan last month, I have discovered that my home server's motherboard is dead. After considering different options, I have realized that I really only need the server to host my RAID1 hard disks, where I store all my photos and other content.

So that's how I got my Synology DS212J NAS, which is an Linux-powered device with low level access in case it is needed. Now the problem was, how to get my 2 HDDs running in that box with preserving all the data.

Unfortunately, the first install of the box requires wiping of the data on the HDD. Fortunately, I have RAID1 setup with two exact copies of all the data, so I decided to sacrifice one of the disks to install the firmware and later insert the second one and copy the data over.

Now, the problem was that my data was on a XFS partition, which DS212J doesn't support by default - it uses EXT4 for its partitions.

Fortunately, Synology is kind enough to provide an SDK which makes it possible to build missing kernel modules and enable more features on the device.

Here is how to do it:

1. Enable terminal access in the web interface of the device - then you can login to the box using ssh root@diskstation.local or whatever name/IP you have given it
2. Go to http://sourceforge.net/projects/dsgpl/ - click Files
3. Download the DSM tool chains (gcc ARM cross compiler) for your firmware (currently 3.2) - for DS212 it is in the Marvell 88F628x, if you have another model use either /proc/cpuinfo or dmesg to find out your CPU type
4. Download the Synology NAS GPL Source also from sourceforge - this is a huge archive that includes source code of all the kernels that Synology uses (check your kernel version with uname -a, mine uses 2.6.32)
5. Extract both archives to /usr/local (or at least link there) - this is important, because kernel Makefile already points to a cross compiler from the tool chain that should be located there
6. cd /usr/local/source/linux-2.6.32 (from the GPL source archive)
7. Copy the correct kernel config for your device - Syology kernel configs are located in synoconfigs, so for DS212J do this: cp synoconfigs/88f6281 .config
8. make menuconfig to use kernel's menu-based configuration utility (ensure that you have libncurses installed for it to work)
9. In the menu, locate the needed additional drivers (File Systems -> XFS in my case), and press M to enable module compilation
10. Exit and make modules
11. This will compile the required .ko files. XFS driver was in fs/xfs/xfs.ko after compilation was completed, but modinfo fs/xfs/xfs.ko also told me that xfs.ko depends on the exportfs.ko as well.
12. I needed to copy both modules to the device, xfs.ko and fs/exportfs/exportfs.ko to make it work, otherwise kernel refused to load the xfs module. To copy the files, use either FTP (enable from the web interface) or the web interface itself. It doesn't matter where you put them.
13. Login to the device with ssh root@diskstation.local again (note, you need to be root, not admin)
14. Go to the directory where you uploaded the .ko files (cd /volume1/public in my case)
15. Load the modules: insmod exportfs.ko, then insmod xfs.ko - if it doesn't complain, then you have XFS support enabled (or whatever other driver you needed to load)
16. Then create a directory anywhere and mount your second HDD to it, then copy the files with cp or rsync. Example: mount -t xfs /dev/hda storage - look which name did you HDD receive. Mine was hda, because I have installed the firmare to hdb before. Check mount without the arguments on where you firmware is located. Also, my disk didn't have a partition table, only a single partition starting in MBR, that's why I used /dev/hda there and not /dev/hda1 or something. Use parted /dev/hda for more info which partitions you have.
17. Rsync is a great way to copy the files then, eg rsync -arv storage/ /volume1/ - this will preserve all file attributes
18. When copying is complete, add the second HDD to the Synology RAID using the web interface

Note: fortunately I didn't have to replace the stock kernel fully on the device. It was enough to load these two new modules. However at first, when loading of only xfs.ko failed due to missing symbols, I already thought that I need to do that, and I have even tried with no help (before discovering that I actually need to load exportfs.ko). 

FYI: Synology's kernel is located in the flash memory, not on the HDD as the rest of the system. The devices with flash partitions are /dev/mtd*, with /dev/mtd0 being the boot loader (don't touch this one - it provides the ability to install the rest of the firmare with Synology Assistant over the network) and /dev/mtd1 being the uImage of the kernel.

If you still need to replace the kernel, you may try to make uImage of the kernel (make sure you have uboot installed for this to work - this is what Synology uses), copy tyhe uImage file to the device and then cat uImage > /dev/mtd1 - but do it at your own risk, I am not sure whether will Synology Assistant work if you flash the wrong kernel and reboot. I guess it should, but I haven't tested it :-)

Hopefully it will be useful for someone - the same way you can add support for Apple/Mac HFS filesystem, ReiserFS or others.