Understanding ESXi root disk partitions.

After the installation of ESXi if we have look at partition of the disk which is used for installation of ESXi we will find 5 partitions on it. In this article I am covering some brief idea about size calculation and significance of each partition.

Take the putty session to ESXi.

We will find couple of partitions on that disk. What are these partitions ?

~ # partedUtil getptbl /dev/disks/mpx.vmhba1\:C0\:T0\:L0
261 255 63 4194304
1 64 8191 C12A7328F81F11D2BA4B00A0C93EC93B systemPartition 128
5 8224 520191 EBD0A0A2B9E5443387C068B6B72699C7 linuxNative 0
6 520224 1032191 EBD0A0A2B9E5443387C068B6B72699C7 linuxNative 0
7 1032224 1257471 9D27538040AD11DBBF97000C2911D1B8 vmkDiagnostic 0
8 1257504 1843199 EBD0A0A2B9E5443387C068B6B72699C7 linuxNative 0

Now see the output of df -h you will see that along with VMFS datastores there are vfat file systems mounted in it.

~ # df -h
Filesystem   Size   Used Available Use% Mounted on
VMFS-5      29.8G  10.7G     19.0G  36% /vmfs/volumes/ISCSIDataStore-2
VMFS-5      19.8G   4.2G     15.5G  21% /vmfs/volumes/ISCSIDatastore-1
VMFS-5      19.8G   1.0G     18.7G   5% /vmfs/volumes/LocalDataStore-1
vfat       249.7M 157.8M     91.9M  63% /vmfs/volumes/e848f979-a81f576c-bb22-bc4cffa55d54
vfat       249.7M 173.3M     76.5M  69% /vmfs/volumes/4c129273-503f4af7-8e7a-d63e665c5ea0
vfat       285.8M 192.6M     93.2M  67% /vmfs/volumes/540c641b-75203ae6-8a13-000c29bcb49e

Why I am seeing 3 partitions mounted instead of 5 as per partedUtil output ?

These vfat file systems are partition of the ESXi. Now if you compare the output with partedUtil command you will see only three partitions are mounted in output of df. These partitions are of type “linuxNative”. Now if you see paredUtil command has 3 “linuxNative” partitions which are showing mounted in df.

How to calculate the size of partition from output of paredUtil ?

If we take look at output of partedUtil you will see 5 partitions in it. Now let me take 1 partition as an example to calculate the size.

1 64 8191 C12A7328F81F11D2BA4B00A0C93EC93B systemPartition 128

Taking second and third column
Starting value = 64 and Ending Value = 8191
Formula for calculation in MB is = ( Ending Value – Starting Value )/2*1024
In this case it will become = ( 8191 – 64) / 2 * 1024 which comes approx 4 MB

What are the significance of these 5 partitions ?

We will start in same order in which they are displaying in output of partedUtil.

Partition 1 : First partition contains the boot loader which runs when the host boots up. Size is 4MB.

Partition 5 : It contains the core hypervisor code. Which is packaged into several files. Size is 249 MB(approx)

Partition 6 : It contains the copy of partition 5 Once an update is applied we are having one safe copy in another partition. Size is 249 MB(approx)

Partition 7 : It is used to hold diagnostic core dumps.Size is 110 MB.

Partition 8 : It contains the vmware tools ISO. This contains the auxiliary files. Size is 286 MB (approx)



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