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原帖由 lizhi_wang 于 2007-7-13 20:56 发表 ![]()
What is WAFL?
What are the main features that WAFL can provide?
What is snapshot?
Describe how to do snapshot in WAFL.
How does WAFL improve performance?
What design does WALF ...
What are the main features that WAFL can provide?
WAFL is a UNIX compatible file system optimized for network file access. In many ways WAFL is similar to other UNIX file systems such as the Berkeley Fast File System (FFS) and TransArc's Episode file system. WAFL is a block-based file system that uses inodes to describe files. It uses 4 KB blocks with no fragments.
WAFL is short for Write Anywhere File Layout which means it writes meta-data anywhere on disk.
What is snapshot?
WAFL's primary distinguishing characteristic is Snapshots, which are read-only copies of the entire file system. WAFL creates and deletes Snapshots automatically at prescheduled times, and it keeps up to 255 Snapshots on-line at once to provide easy access to old versions of files.
Describe how to do snapshot in WAFL.
Simply duplicates the root inode.
How does WAFL improve performance?
Putting both the data and its inode right next to each other on disk.
Since WAFL can write meta-data anywhere on disk, it can optimize writes more creatively.
WAFL can write blocks to disk in any order.
WAFL can allocate disk space for many NFS operations at once in a single write episode,it gathers up hundreds of NFS requests before scheduling a consistency point, at which time it allocates blocks for all requests in the consistency point at once.
What design does WAFL use to avoid the system failure caused by a power outage?
WAFL uses non-volatile RAM to keep a log of I/O requests it has processed since the last consistency point.,NVRAM is special memory with batteries that allow it to store data even when system power is off. After an unclean shutdown, WAFL replays any requests in the log to prevent them from being lost.
[ 本帖最后由 滋毛儿 于 2007-7-16 10:35 编辑 ] |
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楼主: 滋毛儿
发表于 2007-06-29 13:15
