Re: [sot] file times / file metadata

From	cross@spitfire.i.gajendra.net (Dan Cross)
Newsgroups	comp.lang.c
Subject	Re: [sot] file times / file metadata
Date	2017-11-29 21:01 +0000
Organization	PANIX Public Access Internet and UNIX, NYC
Message-ID	<ovn77c$41o$1@reader2.panix.com> (permalink)
References	<5a91718b-b272-4cdf-adfd-8f6777851b23@googlegroups.com> <ov61fa$dgk$1@dont-email.me> <ovk4la$7di$1@reader2.panix.com> <ovlthi$ptt$1@dont-email.me>

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In article <ovlthi$ptt$1@dont-email.me>,
David Brown  <david.brown@hesbynett.no> wrote:
>I think many people have a concept that a "copy" must in some way be
>/physically/ independent of the original.  In reality, copies are often
>just logical copies - they act as though they are independent in storage
>somewhere, but they might not be.  They might be CoW copies, or stored
>on something with deduplication.  Even if they are supposedly
>independent copies on different disk sectors, they might be on the same
>physical disk or the same file system, and therefore not independent.
>And you can go the other way - a file may appear to be a single logical
>file, but have multiple physical copies (such as on a RAID system).

Yes, that's the intuition. I suspect that Stuckle thinks of a "copy"
as something one puts on a 5.25" floppy disk and then trades to the
kid down the street for an old copy of Sports Illustrated.

>To me, a "copy" is a logical operation.  It means that when everything
>is working as it should - no disk failures, server room fires,
>filesystem corruption, human error - you have two logically independent
>versions of the file or object.  If you want something that protects
>your data against one or more type of failure, it is a "backup".

Yes; I agree.

>> This came up when Plan 9 moved the filesystem to the Venti
>> storage server.  Venti uses content-addressible storage: blocks
>> are hashed using a cryptographically-secure hashing algorithm,
>> and a mapping from hash to block is kept in an index volume.
>> When writing to the store, an attempt is made to look up the
>> block's hash in the index; if an entry already exists, one
>> assumes the block data is already present and returns success.
>> Otherwise, a block is allocated, the data are written to the
>> newly-allocated block, and the (hash, block address) pair is
>> added to the index.
>
>That is probably quite a space-efficient way to store things, perhaps at
>some cost in speed.

Indeed. However, the file server was a dedicated machine on the
network, and it was found that it could still saturate the network
interface. Furthermore, there was a write-cache placed in front of
Venti to amortize the cost of transient storage.

>> [snip]

 	- Dan C.

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Thread

[sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-21 11:50 -0800
  Re: [sot] file times / file metadata "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-11-21 21:05 +0100
    Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-22 09:15 +1300
    Re: [sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-21 12:23 -0800
      Re: [sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-21 12:42 -0800
        Re: [sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-21 13:01 -0800
        Re: [sot] file times / file metadata "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-11-21 22:04 +0100
          Re: [sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-21 13:17 -0800
          Re: [sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-21 13:22 -0800
            Re: [sot] file times / file metadata "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-11-21 23:23 +0100
              Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-22 11:34 +1300
              Re: [sot] file times / file metadata Lew Pitcher <lew.pitcher@digitalfreehold.ca> - 2017-11-21 17:34 -0500
              Re: [sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-21 16:16 -0800
                Re: [sot] file times / file metadata "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-11-22 01:44 +0100
                Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-22 14:10 +1300
                Re: [sot] file times / file metadata gordonb.eiy78@burditt.org (Gordon Burditt) - 2017-11-28 01:55 -0600
          Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-22 11:07 +0100
            Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-22 09:13 -0500
              Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-22 15:50 +0100
                Re: [sot] file times / file metadata jameskuyper@verizon.net - 2017-11-22 07:08 -0800
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-22 16:22 +0100
                Re: [sot] file times / file metadata bartc <bc@freeuk.com> - 2017-11-22 15:37 +0000
                Re: [sot] file times / file metadata bartc <bc@freeuk.com> - 2017-11-22 15:43 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-22 15:01 -0500
                Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-23 17:52 +1300
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-23 14:12 -0500
                Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-24 08:28 +1300
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-24 08:52 -0500
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-23 09:39 +0100
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-23 14:17 -0500
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-11-28 16:44 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-28 14:23 -0500
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-11-28 19:35 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-30 15:54 -0500
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-11-30 21:43 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-12-04 11:42 -0500
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-12-04 19:35 +0000
                Re: [sot] file times / file metadata Keith Thompson <kst-u@mib.org> - 2017-12-04 11:53 -0800
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-12-04 20:11 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-12-04 15:03 -0500
                Re: [sot] file times / file metadata scott@slp53.sl.home (Scott Lurndal) - 2017-11-28 19:42 +0000
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-11-28 20:13 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-30 15:57 -0500
                Re: [sot] file times / file metadata scott@slp53.sl.home (Scott Lurndal) - 2017-11-30 21:17 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-12-04 11:56 -0500
                Re: [sot] file times / file metadata scott@slp53.sl.home (Scott Lurndal) - 2017-12-04 18:36 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-12-04 15:07 -0500
                Re: [sot] file times / file metadata scott@slp53.sl.home (Scott Lurndal) - 2017-12-04 22:27 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-12-04 17:57 -0500
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-12-05 08:50 +0100
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-12-05 08:49 -0500
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-12-05 15:17 +0100
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-12-05 16:32 -0500
                Re: [sot] file times / file metadata scott@slp53.sl.home (Scott Lurndal) - 2017-12-05 15:29 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-12-05 16:37 -0500
                Re: [sot] file times / file metadata scott@slp53.sl.home (Scott Lurndal) - 2017-12-06 01:26 +0000
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-12-06 12:38 -0500
                Re: [sot] file times / file metadata scott@slp53.sl.home (Scott Lurndal) - 2017-12-06 01:27 +0000
                Re: [sot] file times / file metadata jameskuyper@verizon.net - 2017-11-28 09:35 -0800
                Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-29 08:24 +1300
                Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-29 08:27 +1300
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-28 14:29 -0500
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-29 09:51 +0100
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-30 15:59 -0500
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-29 10:00 +0100
                Re: [sot] file times / file metadata "James R. Kuyper" <jameskuyper@verizon.net> - 2017-11-29 09:11 -0500
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-29 15:28 +0100
                Re: [sot] file times / file metadata "James R. Kuyper" <jameskuyper@verizon.net> - 2017-11-29 11:32 -0500
                Re: [sot] file times / file metadata James Kuyper <jameskuyper@verizon.net> - 2017-11-23 15:05 -0500
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-24 10:20 +0100
                Re: [sot] file times / file metadata Jerry Stuckle <jstucklex@attglobal.net> - 2017-11-24 09:05 -0500
                Re: [sot] file times / file metadata Robert Wessel <robertwessel2@yahoo.com> - 2017-11-24 22:50 -0600
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-11-28 16:59 +0000
                Re: [sot] file times / file metadata Ian Collins <ian-news@hotmail.com> - 2017-11-29 08:26 +1300
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-29 10:10 +0100
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-11-29 21:01 +0000
                Re: [sot] file times / file metadata David Brown <david.brown@hesbynett.no> - 2017-11-29 23:13 +0100
                Re: [sot] file times / file metadata cross@spitfire.i.gajendra.net (Dan Cross) - 2017-11-30 17:26 +0000
              Re: [sot] file times / file metadata fir <profesor.fir@gmail.com> - 2017-11-22 08:00 -0800
              Re: [sot] file times / file metadata "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-11-22 17:11 +0100
            Re: [sot] file times / file metadata "Pascal J. Bourguignon" <pjb@informatimago.com> - 2017-11-22 16:51 +0100
              Re: [sot] file times / file metadata scott@slp53.sl.home (Scott Lurndal) - 2017-11-22 16:36 +0000

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