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

[John Nemeth <jnemeth%cue.bc.ca@localhost>]

On Jun 21, 12:03pm, Stephen Borrill wrote:
} On Thu, 19 Jun 2014, Greg Troxel wrote:
} > Gerard Lally <lists+netbsd.users%netmail.ie@localhost> 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
} 5.1_STABLE
} 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.

     GPT partitions can be resized in -current.  However, there is
no kernel support for resizing wedges, so you need to dkctl delwedge
first, then dkctl addwedge afterwards.  And, of course, there has
to be space after the end of the wedge in order to increase the
size.  gpt(8) will not move data around by itself.

     BTW, there is an issue in the LVM code somewhere when it comes
to handling large volumes.  I tried to create a large LV (I think
around 6T) and if I recall right it got truncated down to 2T.

}-- End of excerpt from Stephen Borrill