Operating Systems 2019W Lecture 10 - Revision history

Soma: /* Readings */

2019-02-07T00:48:05Z

Readings

← Older revision		Revision as of 00:48, 7 February 2019
Line 5:		Line 5:
	==Readings==		==Readings==

			There are a number of chapters in the textbook related to filesystems & block devices. You are not responsible for all of this material, but you may benefit from looking through the following for key concepts covered in class - particularly if you are confused about some of the concepts.

			* [http://pages.cs.wisc.edu/~remzi/OSTEP/file-devices.pdf I/O Devices]
			* [http://pages.cs.wisc.edu/~remzi/OSTEP/file-disks.pdf Hard disk drives]
			* [http://pages.cs.wisc.edu/~remzi/OSTEP/file-intro.pdf Files and Directories]
			* [http://pages.cs.wisc.edu/~remzi/OSTEP/file-implementation.pdf Filesystem implementation]
			* [http://pages.cs.wisc.edu/~remzi/OSTEP/file-journaling.pdf FSCK and Journaling]

	==Notes==		==Notes==

Soma: /* Notes */

2019-02-07T00:44:32Z

Notes

← Older revision		Revision as of 00:44, 7 February 2019
Line 8:		Line 8:

	==Notes==		==Notes==

			===In Class===
			<pre>
			Lecture 10
			----------

			What is a filesystem?
			- hierarchy of files?
			- may or may not have underlying storage
			- more formally, hierarchical key-value store

			Really, from the kernel's perspective, it is
			- functions that can be called to implement filesystem-related system calls

			This abstraction is knows as the "virtual filesystem", VFS


			In tutorial 4, you're making and manipulating filesystems...stored in block devices


			Examples:
			/proc proc filesystem
			/sys sys filesystem
			/ ext4 filesystem
			/boot/efi vfat filesystem
			/boot ext2 filesystem
			...

			/boot/efi/UBUNTU <-- what filesystem is this on?

			mounting is how we associate a subtree (directory) with a filesystem


			BAD IDEA

			mount /dev/sdc1 /
			(assume /dev/sdc is a USB stick)


			local, persistent filesystems are normally associated with block devices
			- the filesystem is what allows us to use a block device to store files

			a block device is a persistent "array" of "blocks"
			- blocks are fixed size (i.e. 4K)
			- accessed by index

			From a storage perspective, a filesystem is a way of storing a file hierarchy on a block device (i.e., in blocks accessed by indices)



			So is a filesystem just a tree?
			- kind of

			Goals for an on-disk filesystem structure
			- fault tolerant
			- reliable
			- high performance
			- takes the characteristics of the block device into account

			Normally, block devices (whether hard drives or SSDs)
			- sequential access is faster than random access


			High level action on an open system call

			* process makes open system call, e.g. open("/home/student/foo.txt", ...)
			* kernel figures out what filesystem /home/student/foo.txt is on
			(ext4 from /dev/sda2 mounted on /home)
			* kernel calls ext4 open function for /dev/sda2, gives it /student/foo
			* ext4 looks at /dev/sda2, figures out where the blocks are for /student/foo
			* ext4 stores this info in file structure, returns
			<-- what a file descriptor refers to
			</pre>

Soma: Created page with "==Video== The video for the lecture given on February 6, 2019 [https://homeostasis.scs.carleton.ca/~soma/os-2019w/lectures/comp3000-2019w-lec10-20190206.m4v is now available]..."

2019-02-07T00:43:30Z

Created page with "==Video== The video for the lecture given on February 6, 2019 [https://homeostasis.scs.carleton.ca/~soma/os-2019w/lectures/comp3000-2019w-lec10-20190206.m4v is now available]..."

New page

==Video==

The video for the lecture given on February 6, 2019 [https://homeostasis.scs.carleton.ca/~soma/os-2019w/lectures/comp3000-2019w-lec10-20190206.m4v is now available].

==Readings==

==Notes==