some questions about disk partitioning and filesystems and booting

[David Christensen]

On 2020-02-13 07:02, tech-lists wrote:
> Hi,
> 
> [1]
> When a new (12.x) amd64 system is installed, the partition defaults to 
> MBR. I
> normally use this as it's the default. I don't run mixed-OS systems; 
> they are
> all freebsd. But I understand that GPT is newer or "better"?
> 
> If GPT is "better" then why is it not the default?
> 
> My use case is always ufs for the OS and zfs for data. Would it be 
> "better" to
> use GPT when installing a system?

I put my operating system installations on single, small 2.5" SATA SSD's 
and I put 2.5" SATA trayless disk bays in my computers.  This both 
facilitates imaging and allows me to mix and match as required.


For FreeBSD, I use ZFS throughout.


Not all of my computers support booting from GPT, so I use MBR for 
system drives.


The default FreeBSD installer wants to use the entire disk, so I hacked 
the memstick installer and/or choose the following in the installer:

- 1 MiB alignment for everything

- 14 GiB slice

- 2 GiB boot partition, copies=2

- 2 GiB swap partition, mirrored

- 10 GiB root partition, copies=2


The most obvious downside is that MBR does not support labels.  So, the 
FreeBSD boot system uses device node names.  This means I have to ensure 
that the system drive is always ada0 -- during install, whenever I move 
the drive to another machine, and whenever I add or remove drives or 
controllers.  If the drive comes up as the wrong device node, I move 
SATA cables around.


> [2]
> The bsdinstaller defaults to 4GB swap. Isn't this insufficient on a 32GB
> system? Doesn't swap need to be 2x RAM on a fast disk?
> 
> The next install I do I'm thinking of making 2x 32GB swap partitions. These
> being on the same SSD as the base OS. Would you consider this to be
> suboptimal, and if so, why?

In the past, I tried running systems without swap.  They crashed.


My current preference is to have plenty of RAM and a nominal swap partition.


One possibility might be to install with a small swap partition now and 
put a large dummy partition at the end in case you need more swap later. 
  Then again, if your workload does require a lot of swap, you could add 
a dedicated swap device and disable the swap partition on the system drive.


David