Filesystem migration to ext4

As part of our ongoing platform improvement, we will migrate ext3 filesystems to the ext4 format. The migration requires an off-line filesystem check and thus a little downtime for each machine to reboot.

The downtimes will be scheduled individually according to the agreed maintenance windows. We will inform the technical contacts about the exact times for their VMs in advance. Please write to our support if any reboot time does not fit.

Benefits of the new filesystem

The ext4 filesystem offers a number of advantages over the old ext3 filesystem:

• Reduced filesystem check time: this means that both planned machine reboots and error recovery after outages will be sped up significantly.
• Large file handling: access to large files like ZODB databases require less system overhead.
• Large directory handling: file lookup in directories that contain a lot of files is more efficient.
• More subtle run-time optimizations like delayed allocation and others.

After the VMs' disks have been migrated to the new format, applications will benefit from the performance optimizations incrementally as their files are modified. ZODB databases are usually packed once a week, so they will pick up the new on-disk format automatically. Blob directories and PostgreSQL databases will use the new on-disk format only for newly written data. We can assist users with the conversion of old data on request.

Except for the reboot, the change will be completely transparent.