From 444d7c4c16652c833709157bdddbefb62fbfbc07 Mon Sep 17 00:00:00 2001 From: mo khan Date: Sat, 22 May 2021 17:00:02 -0600 Subject: add chapter 12 notes --- doc/10.md | 1 - doc/12.md | 48 ++++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 48 insertions(+), 1 deletion(-) create mode 100644 doc/12.md (limited to 'doc') diff --git a/doc/10.md b/doc/10.md index cb61f5d..4db38f0 100644 --- a/doc/10.md +++ b/doc/10.md @@ -1,4 +1,3 @@ - ## Disk Scheduling One of the responsibilities of the operating system is to use the hardware efficiently. diff --git a/doc/12.md b/doc/12.md new file mode 100644 index 0000000..5c6ffca --- /dev/null +++ b/doc/12.md @@ -0,0 +1,48 @@ +# File-System Implementation + +## Efficiency and Performance + +### Efficiency + +* efficient use of disk space depends heavily on disk-allocation and directory algorithms. +* UNIX inodes are preallocated on a volume. +* empty disk has a percentage of its space lost to inodes. + +## Log structured file systems + +* log based transaction oriented (or journaling) file systems for consistency checking. +* a circular buffer writes to the end of its space and then continues at the beginning, overwriting older values as it goes. + +# Summary + +The file system resides permanently on secondary storage, which is designed to hold a large amount of data permanently. +The most common secondary-storage medium is the disk. + +Physical disks may be segmented into partitions to control media use and to allow multiple, possibly varying, file systems on a single spindle. +These file systems are mounted onto a logical file system architecture to make them available for use. + +File systems are often implemented in a layered or moduluar structure. +The lower levels deal with the physical properties of storage devices. +Upper levels deal with symbolic file names and logical properties of files. +Intermediate levels map the logical file concepts into physical device properties. + +Files can be allocated space on disk in three ways: + +* contiguous + * suffers from external fragmentation +* linked + * direct access is bad +* indexed allocation + * overhead for the index block. + +free space allocation methods influence efficiency of disk-space use, perf of file system and reliability of secondary storage. + +A hash table is commonly used because it is fast and efficient. +However, damage to the table can result in inconsistency between directory info and content. + +Consistency checker can be used to repair damage. + +NFS uses client-server methodology to allow users to access files and directories from remote machines. + +Log structures and caching help improve performance, while log structures and RAID improve reliability. +The WAFL file system is an example of optimization of performance to match a specified I/O load. -- cgit v1.2.3