Date: Wed, 13 Oct 1999 09:52:46 -0700 (PDT) From: David Wolfskill <dhw@whistle.com> To: freebsd-newbies@FreeBSD.ORG, rothenberg@automationonline.com, u98jobj@stud.hh.se Subject: Re: SV: Disks...? Message-ID: <199910131652.JAA31298@pau-amma.whistle.com> In-Reply-To: <000501bf1595$49bb8640$b1102fc2@gsten.hh.se>
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>From: =?iso-8859-1?B?Sm9lbCBCavZyaw==?= <u98jobj@stud.hh.se> >Date: Wed, 13 Oct 1999 18:09:11 +0200 >Read the installation chapter. >It tells you how to link the /var and /tmp dir. Good advice, generally.... >All slice are mounted on the / dir except for the swap slice so the only problem you can have if you follow the directions in Complete FreeBSD is that your root directory fills up but that won't normally happen. But here we're venturing into dangerous territory... and why we try to avoid dealing with -questions material on -newbies. Briefly, in UNIX (generally): * File systems are "mounted" at "mount points" (which are created as directories in the "parent" file systems). So we have a "root" file system, /; it has some files (like /kernel) and some directories (like /dev, /etc, and /usr). Some of these directories contain files and (sub-directories), such as /etc. Some are often (traditinally) empty, such as /usr and /mnt. It is these latter directories that are used as "mount points" -- the "mount" process grafts an entire file system onto the tree at the mount point, so a person or a process that is using the system merely refers to a (relative or absolute) path name for a file, and the system takes care of dealing with which file system(s) get used to get there. It is, however, not usually necessary to split the available disk up into separate file systems. (Historically, this was done in large part because a "big" disk was 600 MB, and the only way you could get a large amount of disk space that was usable for the entire system was to have lots of spinning disks. It would have been possible to have created a "super file system" that would make use of multiple disk drives, but that was sufficiently complicated that it was fairly specialized -- and pretty recent in the history of UNIX (which is about 30 years old). And you can actually mount a new file system onto a non-empty directory, but I mention this more for completeness. It may have some uses, but they tend to be out of the mainstream. [Yes, I've done it, deliberately. In my case, it was a gross hack to circumvent a vendor's shortcoming in the infrastructure needed for the "restore" program.] * It is not necessary to only use a directory in / as a mount point. Whether or not it is desirable depends on the circumstances. For example, I will often make /usr/local a physically separate disk drive, with its file system mounted on /usr (which, in turn, is mounted on /). The reason for this is that it makes a *very* clear separation between the OS and things I've been tweaking: when it comes time to upgrade the OS, I don't even need /usr/local connected to the system -- that way, I *know* the upgrade can't trash it. (Granted, this is referring more to how I do things in non-FreeBSD systems.) As to "slices" -- FreeBSD is the first UNIX version I've used where the concept applies. (Solaris 2.x uses the term about half the time to refer to partitions, and the other half still uses "partition". For example, within "format", one uses the "partition" command to get to the place for defining "slices" Go figure.) And slices are not mounted; file systems are. Slices are regions of disk where (UNIX) partitions are created; partitions may be used for swap, for file systems, or left for raw access by specialized programs (like databases). And just in case anyone might get confused on the topic, swap space isn't mounted, period. (And you do *NOT* want to have overlapping active file systems, or active file systems that overlap active swap space, or overlapping active swap spaces. That way lies disaster.) Cheers, david -- David Wolfskill dhw@whistle.com UNIX System Administrator voice: (650) 577-7158 pager: (888) 347-0197 FAX: (650) 372-5915 To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-newbies" in the body of the message
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