gmirror, gpart and MBR vs GPT in the Handbook
the.lists at mgm51.com
Mon Dec 2 17:35:07 UTC 2013
On 12/2/2013 at 6:26 PM Polytropon wrote:
|On Mon, 02 Dec 2013 12:13:32 -0500, Mike. wrote:
|> My understanding is that MBR can be used with drives only up
|> and including 2TB in size. So if I use MBR, the maximum
|> size I could use would be 2TB. Is that correct?
|Don't confuse partitioning schemes and file systems. Both are
|different things, happening on different "layers". To make it
|simpler than it probably is:
| a) MBR with classic tools (fdisk, bsdlabel)
| b) MBR with modern tool (gpart)
| c) GPT (gpart)
| d) Dedicated (only the "bsdlabel part")
|RAID concepts =
| a) mirror
| b) stripe
| c) combined and extended forms ...
|File system =
| a) UFS
| option +U: soft updates
| option +J: journal
| b) ZFS
|Of course ZFS can handle things like "RAID concepts" already
|internally, whereas UFS would use gstripe and gmirror as
|"little helpers" - it will run on top of them, i. e., you
|initialize the device that represents the whole mirror
|instead of individually dealing with the drives that the
|mirror is constructed of.
|Regarding UFS's 2 TB limitation:
|Additionally, MBR can be troublesome on bigger hard disks
|Today's consensus seems to be:
|If you use ZFS, let ZFS deal with everything.
|If you use UFS, use gpart for preparation work. Use GPT when
|possible, MBR only in exceptions, and dedicated if and only
|if you really _really_ know what you're doing. :-)
Following the bsdinstall-partitioning link you cited, and then
following a link on that page, I wind up here:
"...The organization of the partition table in the MBR limits
the maximum addressable storage space of a disk to 2 TB ...."
That (and other places) is where I got the 2TB limit of MBR into
my head. Am I misunderstanding that statement?
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