ZFS Balancer

A PHP script created in order to re-balance a ZFS RAID array that was built up over time by adding drives to an existing pool.

To check the balance of your current pool, use the command:

zpool list -v

Here is an example output of my very unbalanced pool soon after I added two 8TB drives to it:

NAME   SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
zpool1  13.6T  4.21T  9.39T         -    15%    30%  1.00x  ONLINE  -
  mirror  3.62T  2.20T  1.43T         -    31%    60%
    sda      -      -      -         -      -      -
    sdb      -      -      -         -      -      -
  mirror  2.72T  1.65T  1.07T         -    32%    60%
    sdc      -      -      -         -      -      -
    sdd      -      -      -         -      -      -
  mirror  7.25T   368G  6.89T         -     2%     4%
    sde      -      -      -         -      -      -
    sdf      -      -      -         -      -      -

And this is what it is like today much later and balanced:

NAME   SIZE  ALLOC   FREE  EXPANDSZ   FRAG    CAP  DEDUP  HEALTH  ALTROOT
zpool1  13.6T  9.84T  3.75T         -    25%    72%  1.00x  DEGRADED  -
  mirror  3.62T  2.62T  1.01T         -    26%    72%
    ata-WDC_WD40EFRX-68WT0N0_WD-WCC4E1984538      -      -      -         -      -      -
    ata-WDC_WD40EFRX-68WT0N0_WD-WCC4E1984290      -      -      -         -      -      -
  mirror  2.72T  1.93T   807G         -    29%    71%
    ata-WDC_WD30EFRX-68EUZN0_WD-WCC4N1DCX6L4      -      -      -         -      -      -
    ata-WDC_WD30EFRX-68EUZN0_WD-WMC4N1605537      -      -      -         -      -      -
  mirror  7.25T  5.29T  1.96T         -    24%    73%
    ata-WDC_WD80EFZX-68UW8N0_VLKZKBBV      -      -      -         -      -      -
    ata-WDC_WD80EFZX-68UW8N0_R6G68HBY      -      -      -         -      -      -

Deduplication Off

As this script works by copying files before deleting the original and renaming the copy back to that of the original, so you probably need deduplication switched off for the principle to properly work. You can do this in Ubuntu 16.04 with the following command:

sudo zfs set dedup=off myZpoolName

Note: this script will work on one file at a time rather than all at once, so it's not a disaster if you terminate the script mid-way through. The worst thing that could happen is that you either have the original file and a copy with a number extension, or you just have the copy with a number extension rather than the original, but you never lose/corrupt a file.

Requirements

This script requires PHP 5.5 or higher. You can usually install PHP on Ubuntu 16.04 with

sudo apt-get install php7.0-cli

On Ubuntu 14.04 I believe the command was:

sudo apt-get install php-cli

Usage

php main.php /path/to/folder/to/balance

Note: You can use relative or full paths.

Testing

Tested on Ubuntu 14.04 64bit with php 5.5.9