Apollo will undergo a kernel upgrade on Thursday at 12 AM EST (-0500 GMT) to improve filesystem performance. After local testing, we are pleased to announce that Apollo will continue to provide an innovative hosting platform by using v3 of the Linux kernel. v3 introduces several optimizations and stability improvements over v2.6.35 released in August 2010 that has been used on Apollo since last year.
During this time too, aufs, which provides our filesystem technology will undergo a couple changes. First, direct branch access detection will be disabled to reduce time taken to access a file on a client’s writeable branch. Second, path traversal calculations have been traditionally calculated within the kernel-space instead of user-space to resolve crashes inside directories containing a large number of inodes. Since deploying Apollo in 2009, this problem is no longer reproducible.
This outage is expected to last 30 – 45 minutes during which time the proposed changes will be verified to ensure no complications arise. Maintenance should conclude around 1 AM EST after which time load averages will be monitored to ensure I/O wait spikes dissipate that occur as aufs’ cache is filled then expunged in v2.6.35.