Isilon: What is an Isilon Boot Disk and what does it do

Different Isilon nodes (both old and new) have differing designs for booting.

Old nodes whose models start with a number like 36000X, 12000X, 72NL, 5400S do not have separate boot drives. They have approximately 2GB shaved off each spindle (this is still the case today for backwards compatibility) split into 4x 512MB partitions. These partitions store the entirety of OneFS OS. There is no "bootloader" to load which then boots OneFS (like the boot DOS then load Windows 3.1 philosophy). OneFS is based off FreeBSD and that _is_the OS.

Nodes whose models start with S, X, NL, HD all have boot drives in the chassis. There are two Serial Advanced Technology Attachment (SATA) flash modules that plug into the internal SATA controllers on the motherboard. These now contain the four OneFS partitions. It is also where logs and core dumps are stored (/var/log, /var/crash). Also, these two "drives" are mirrored copies of each other. In this "design," heavy logging to /var/log means that there is more wear on the boot drives.

For the S210/X410/X210/NL410 nodes, there is an NVRAM card. This card includes a flash drive to destage the journal which will allow the node to comeback up after an extended power loss scenario. The Journal is NOT destaged to the boot drives.

The GEN6 Nodes (F800, H600, H500, H400, A200, A2000) boots off boot partitions that exist on the data drives. These drives are protected using Erasure coding to remove the dependency on dedicated boot drives. SSD drives in the GEN6 nodes are used for the journal to remove the dependency on NVRAM. There are multiple, distributed copies of the journal. Although the nodes do not boot off separate drives, the partition layout of OS, logs, and cores remain the same as nodes with physical boot drives.