The first topic in second day of CLSF 2014 is about NFS, which lead by Tao Peng from PrimaryData. The protocol of NFS is updated to 4.2 and the mainly jobs of NFS community is implement many features (such as “server side copy”) which had been used on local file system onto server side.
Then the distributed software developer in Xiaomi —— Liang Xie introduce the basic infrastructure of Xiaomi Cloud Storage and report some severe problems about IO stack. The first problem is that heavy write pressure will cause long latency on ext4 file system, and the latency will be short if the local file system is replaced by xfs.
Zheng Liu (from Alibaba): The implement of journal in xfs is better than ext4. When large mount of write operations come to ext4, it have to write checkpoint in journal and flush disk, which may take a long time. I think you could try ‘no journal’ mode which developed by google guys in ext4.
#note: the way to use no journal mode in ext4
mkfs.ext4 -O ^has_journal, .... /dev/sdx
Another problem is Xiaomi want to use io-scheduler of deadline but they can’t use cgroup by ‘deadline’.
Next topic about ext4 is hold by Zheng Liu. In this year, ext4 has add no new features (may be that’s why it is so stable). In google’s chrome OS, they want to store something like cookie for every user, so it need to add encryption feature in ext4. We ask why chrome os not using encryptfs on ext4. The answer of Zheng Liu is: the requirement is came from google itself, so no one knows why. Ext4 also add a new option “sparse_super2” (to store super block only in the beginning and the end of ext4 groups) and “packed_meta_block” (to squeeze all meta data of ext4 into the beginning of disk, mainly for the SMR disk).
The last topic is about OSv, the most popular and cutting-edge OS in this conference. OSv is a operating system based on virtual machine and cloud environment. It reduce the IO and network stack which makes it very fast and effective. The jvm and some scripts language (such as python, ruby, node.js) could already run on OSv, therefore I consider that it has wined a large part of cloud market for it could run hadoop/spark and many front-end web application.