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Re: GPT questions - gpt reliability, wedge naming, and filesystem scaling.

On Thu, 19 Jun 2014, Greg Troxel wrote:
Gerard Lally <> writes:

1) Is it safe to use GPT on NetBSD? The warnings on the gpt man page
leave me less than 100% confident.

On NetBSD 6, I would say yes.  Even on 5, I think so.   I am not really
clear on booting from GPT, but for other than the boot/root fs it should
be fine.  I have multiple systems with gpt disks and no issues.

I have used it on -5 for a long time. I have also got GPT booting working on -5 by compiling the -6 gpt sources on -5 (with minimal hacking). The trick is not to read the man pages, then you won't know it's not supposed to work :-)

backup1# uname -r
backup1# gpt show ld0
       start        size  index  contents
           0           1         PMBR
           1           1         Pri GPT header
           2          32         Pri GPT table
          34          30
          64    20971520      1  GPT part - NetBSD UFS/UFS2
    20971584     8388608      2  GPT part - NetBSD swap
    29360192  9736507256      3  GPT part - NetBSD UFS/UFS2
  9765867448          39
  9765867487          32         Sec GPT table
  9765867519           1         Sec GPT header
backup1# df
Filesystem   1K-blocks       Used      Avail %Cap Mounted on
/dev/dk0       10323036    4293292    5513596  43% /
tmpfs              1424        348       1076  24% /dev
/dev/dk2     4792839924 2848287660 1704910268  62% /backup
kernfs                1          1          0 100% /kern
ptyfs                 1          1          0 100% /dev/pts
procfs                4          4          0 100% /proc

2) As I understand it the NetBSD FFS filesystem is capable of growing
to 8 zettabytes, but MBR partitioning combined with traditional
disklabels meant we were restricted to 2 (or 4) TB partitions in
practice. Am I right in saying that GPT and wedges remove this
restriction, and we can now create partitions and filesystems greater
than 4TB?

I think disklabels are limited to 2TB; I'm not sure if it's the whole
disk or per partition.  (Maybe that's 4TB.)  That is correct - GPT does
not have a 2TB limit.

See above. The thing I find annoying is that wedges/gpt partitions cannot be resized. For this reason, when I move the relevant machines to -6 I'll use lvm.


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