[PVE-User] Proxmox VE 3.4 and ZFS: Using compression=lz4 instead of compression=on by default

[Daniel Mettler]

Servus!

My questions:
*************

1) Will there soon be a Proxmox VE ISO that uses lz4 for transparent ZFS compression by default, i.e. at installation time already?

2) Is there any documentation on how the Proxmox VE 3.4 ISO image is being built/created (particularly, how it's made bootable)?

3) Why isn't it possible to activate and use other consoles (e.g. by hitting CTRL-ALT-F4) during the Proxmox VE installation? Or is it possible?

Background:
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I tried various workarounds to make Proxmox VE 3.4 use compression=lz4 for ZFS at installation time already (reason: lz4 is considered the best choice for ZFS compression algorithm in most cases. AFAIK, ZoL still uses lzjb by default, but there are plans to move to lz4 soon).

I finally decided, the best way for us to go is creating a bootable, patched ISO based on the original Proxmox VE 3.4 ISO.

Here’s how I created the patched ISO:

1. Loop-mount the original ISO (can only be mounted read-only):

# mount -o loop /path/to/proxmox-ve_3.4-3f2d890e-1.iso /mnt/cdrom

2. Copy /usr/bin/proxinstall from the mounted ISO image to a read-writeable directory (create directories as necessary):

# cp -a /mnt/cdrom/usr/bin/proxinstall /mnt/cdrom_patched/usr/bin/proxinstall

3. Edit the /usr/bin/proxinstall script as follows:

# diff -u ../cdrom/usr/bin/proxinstall usr/bin/proxinstall 
--- ../cdrom/usr/bin/proxinstall	2015-02-12 17:52:50.000000000 +0100
+++ usr/bin/proxinstall	2015-03-17 21:50:07.662031284 +0100
@@ -592,7 +592,7 @@
     # disable atime during insatll
     syscmd ("zfs set atime=off $zfspoolname") == 0 ||
 	die "unable to set zfs properties\n";
-    syscmd ("zfs set compression=on $zfspoolname") == 0 ||
+    syscmd ("zfs set compression=lz4 $zfspoolname") == 0 ||
 	die "unable to set zfs properties\n";
 }

4. Use the complicated but very powerful tool xorriso (install it, if necessary) to create a bootable ISO image based on the original ISO, but with /usr/bin/proxinstall “overwritten” with the edited proxinstall script:

# xorriso -boot_image grub patch -indev proxmox-ve_3.4-3f2d890e-1.iso -overwrite on -outdev proxmox-ve_3.4-3f2d890e-1-with-lz4-patch.iso -blank as_needed -pathspecs on -add /usr/bin/proxinstall=/mnt/cdrom_patched/usr/bin/proxinstall -- -commit

5. Use this patched ISO to install Proxmox VE 3.4 as usual

After rebooting the installed Proxmox VE 3.4 host/server, use the following command to verify that lz4 has been used by default:

# zfs get compression
NAME              PROPERTY     VALUE     SOURCE
rpool             compression  lz4       local
rpool/ROOT        compression  lz4       inherited from rpool
rpool/ROOT/pve-1  compression  lz4       inherited from rpool
rpool/swap        compression  lz4       inherited from rpool

I hope this is of help to other users as well. And of course, that an official ISO implementing this small, but important improvement will be released soon :)

Cheers

Dani

-- 
Daniel Mettler                                 http://www.numlock.ch