RAID and filesystems

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== File System impact ==
 
== File System impact ==
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=== BTRFS ===
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=== EXT ===
  
 
=== XFS ===
 
=== XFS ===

Revision as of 01:50, 14 January 2018

Contents

Raid layout

In order to work efficiently, file systems need to understand the disk structure they are running on. File system tuning is somewhat of an arcane art, and the different variants of mkfs usually contain code to optimise the file system layout to the underlying disks. If the file system is over LVM and/or RAID, the code looks at the setup and optimises the layout.

The important figures to note are the stripe unit and the stripe width. The stripe unit is the size of the data written per disk. This is usually thought of as a multiple of 512 bytes, as that was typically a single block on a disk. A single disk block is now often 4K. But a typical stripe unit will now be of the order of a megabyte. The stripe width is the number of data blocks in a stripe.

For raids 5 & 6, the stripe width is disks-minus-one or disks-minus-two.

For raid 1, the stripe width is 1.

For raid 10, the picture seems rather more complicated.

File System impact

BTRFS

EXT

XFS

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