From: Marcelino Mata (mmata@MULTIMATIC.COM)
Date: Thu Dec 18 2003 - 12:33:05 EST
I am not using General Parallel File System. Standard 4.3.3 with JFS.
Here's some background information on JFS mount options:
JFS uses direct, single indirect, and double indirect disk addressing. The
disk inode contains 9 slots for disk addresses. The first 8 are used for the
direct addressing, while the ninth is used for indirect addressing.
Direct addressing
If the file is les than or equal to 32K, then the file will use direct
addressing, which means the inode will point directly to the data blocks.
Single Indirect addressing
If the file is too larger for direct addressing, it will use a form of
indirect addressing. Single indirect addressing is called when the file's
data blocks can be addressed by a single indirect block. In this case, the
direct block addresses are unused and the indirect block address contains
the disk address of the one and only indirect block. Each 4 byte entry in
the indrect block refers to a data block; therefore, single indirect
addressing is used for files greater than 32K yet less than 4MB.
Double Indirect addressing
If the file is larger than 4 MB, double indirect addressing is used. In this
case, the indirect field contains the block number of the double indirect
block for the file. The double indirect block contains 512 pointers to the
indirect blocks. As stated before, each indirect block contains 1024 block
addresses for the data for the file.
I am told that Multiple Indirect mounting is the default on AIX 5.x. I
believe using multiple indirect allows any of the three to be used.
Marcelino
>-----Original Message-----
>From: Bob.Kelley@BRINKSINC.COM [mailto:Bob.Kelley@BRINKSINC.COM]
>Sent: Thursday, December 18, 2003 12:13 PM
>To: aix-l@Princeton.EDU
>Subject: Re: indirect JFS mount
>
>
>why would that be necessary? are you using GPFS by chance and not JFS?
>
>Bobby Kelley Jr.
>972-877-5341
>
>
>
>|---------+---------------------------->
>| | Marcelino Mata |
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>| | <aix-l@Princeton.|
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>| | AM |
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>| | IBM AIX |
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> | To: aix-l@Princeton.EDU
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> | cc:
>
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> | Subject: indirect JFS mount
>
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>
>We use Netbackup to backup our AIX server and we are
>encountering problems
>which Veritas says can be fixed by us changing our JFS mount option to
>"multiple indirect addressing". Using a command like this "chfs -a
>options=rw,mind /fsname".
>
>
>I am concerned about any negative aspects of changing the default mount
>options on a production server. I have a very low confidence level with
>Veritas's knowledge of AIX filesystems. Has anyone else made changes to
>their systems and can they comment on the pro's and cons' of
>indirect mount
>options?
>
>
>Marcelino
>
>
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