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From: guy@sun.uucp (Guy Harris)
Newsgroups: net.unix-wizards
Subject: Re: tar fs copy
Message-ID: <2819@sun.uucp>
Date: Tue, 24-Sep-85 02:12:51 EDT
Article-I.D.: sun.2819
Posted: Tue Sep 24 02:12:51 1985
Date-Received: Thu, 26-Sep-85 06:22:00 EDT
References: <832@burl.UUCP> <221@drivax.UUCP> <842@burl.UUCP> <240@investor.UUCP> <233@drivax.UUCP> <249@investor.UUCP> <239@drivax.UUCP>
Organization: Sun Microsystems, Inc.
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> Pipes use an inode on the root file system.

Not in systems since V7; in V7, a "pipe device" was added, so that you can
put pipes on other file systems if you want.

Other systems, like 4.2BSD, use mechanisms other than pseudo-files to buffer
pipe data.

> They are limited to 5120 bytes on System V, and 4096 on some other systems,
> by code in the kernel.

To clarify - this is not a limit on the total amount of data which can be
poured down a pipe (which seems to be what the previous poster was worried
about, since they were using something like two piped-together "tar"s to
copy a huge file system).  This is a limit on how much data can be buffered
in a pipe before the writer is blocked.  Chances are slim (if not
nil) that you won't be able to copy a big file system using piped-together
"tar"s because of the pipe filling up the file system (unless, of course,
you're moving data to the file system on which the pipes exist).

	Guy Harris


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