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Re: Defragmenting a RAID 5 volume?

From: Mladen Gogala <>
Date: Wed, 21 Jan 2004 06:39:39 -0800
Message-ID: <>

On 01/21/2004 03:04:26 AM, wrote:

> GB. My question is, can a RAID 5 volume be defragmented? Is it sane,
> technically? The volume is 130GB in size...

You are defragmenting a file system, not a volume. Block based file systems cannot be defragmented, only extent-based file systems can. Block based file systems like UFS or SYSV-1K FS do not have extents, which means that the word "fragmentation" doesn't make sense. You have superblock, inodes and data blocks. You don't have extents. AFAIK NTS is an extent-based file system and it can be defragmented. It is questionable, however, what will you gain by defragmenting. If your files have < n extents, their extent maps are cached in memory and need not to be re-read each time you access files. Hopefully, you're not using an NT system for DW, which means that your I/O pattern consists of random reads/writes, few blocks at a time. Fragmentation hurts you when you are doing frequent multiblock reads which are split into several I/O requests instead of being satisfied by a single large one. As defragmenter moves file extents around, database cannot be accessed, which essentially means that you must shut down the instance or it will hang. I don't know how much will you gain, but yes, you can defragment 130GB file system, even if it's on a Rabid Array of Inefficient Disks. As they say, size doesn't matter, it's the magic in the disk.

Please see the official ORACLE-L FAQ:
Author: Mladen Gogala

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Received on Wed Jan 21 2004 - 08:39:39 CST

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