Ffs - Revision history

Pbug: /* Intro */ link

2008-06-05T13:05:57Z

Intro: link

← Older revision		Revision as of 06:05, 5 June 2008
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	Here in the example the backups are 32, 25032 and 50032. To find out the alternate superblocks after a filesystem has already been created use [[newfs]] -N.		Here in the example the backups are 32, 25032 and 50032. To find out the alternate superblocks after a filesystem has already been created use [[newfs]] -N.

	Next (not counting the super-blocks) the filesystem is split into 2 different parts. One part is data and the other is meta-data(inodes). The way inodes are placed on the disk is original, the cylinders on the disk are placed in cylinder groups and each cylinder group holds inodes and data, inodes at the beginning of the cylinder group and data after. The inodes are the reference points for objects and data in the filesystem and they hold information such as:		Next (not counting the super-blocks) the filesystem is split into 2 different parts. One part is data and the other is meta-data ([[inode\|inodes]]). The way inodes are placed on the disk is original, the cylinders on the disk are placed in cylinder groups and each cylinder group holds inodes and data, inodes at the beginning of the cylinder group and data after. The inodes are the reference points for objects and data in the filesystem and they hold information such as:

	*[[permissions]]		*[[permissions]]

Pbug: /* Intro */ remove broken image

2008-06-05T12:23:06Z

Intro: remove broken image

← Older revision		Revision as of 05:23, 5 June 2008
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	The data an inode holds is also called '''metadata'''. The size of a UFS1 inode is 128 bytes. By default an inode exists for every 8192 bytes of filesystem space, this is tweakable with [[newfs]] when the filesystem is first created. To save the tweaked filesystem in a backup one could use dumpfs with the -m option to dump the exact newfs command to create a similar filesystem (neat feature).		The data an inode holds is also called '''metadata'''. The size of a UFS1 inode is 128 bytes. By default an inode exists for every 8192 bytes of filesystem space, this is tweakable with [[newfs]] when the filesystem is first created. To save the tweaked filesystem in a backup one could use dumpfs with the -m option to dump the exact newfs command to create a similar filesystem (neat feature).

	~~[[Image:ffs.png]]~~


	The inode in FFS does not store the filename, that has to be read out of the data of a directory which contains entries of filenames up to 255 bytes long not including the NUL terminator and also has the inode number stored for reference back to the [[inode]] and thus the data of a file. Lookup always starts at the root of the system which is usually inode number 2 in FFS:		The inode in FFS does not store the filename, that has to be read out of the data of a directory which contains entries of filenames up to 255 bytes long not including the NUL terminator and also has the inode number stored for reference back to the [[inode]] and thus the data of a file. Lookup always starts at the root of the system which is usually inode number 2 in FFS:

Pbug: /* Intro */

2008-06-05T12:21:37Z

Intro

← Older revision		Revision as of 05:21, 5 June 2008
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	*file group		*file group

	The data an inode holds is also called '''metadata'''. The size of a UFS1 inode is 128 bytes. By default an inode exists for every 8192 bytes of filesystem space, this is tweakable with [[newfs]] when the filesystem is first created.		The data an inode holds is also called '''metadata'''. The size of a UFS1 inode is 128 bytes. By default an inode exists for every 8192 bytes of filesystem space, this is tweakable with [[newfs]] when the filesystem is first created. To save the tweaked filesystem in a backup one could use dumpfs with the -m option to dump the exact newfs command to create a similar filesystem (neat feature).

	[[Image:ffs.png]]		[[Image:ffs.png]]

Pbug: /* Intro */ cylinder groups and inodes

2008-06-05T12:15:10Z

Intro: cylinder groups and inodes

← Older revision		Revision as of 05:15, 5 June 2008
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	Here in the example the backups are 32, 25032 and 50032. To find out the alternate superblocks after a filesystem has already been created use [[newfs]] -N.		Here in the example the backups are 32, 25032 and 50032. To find out the alternate superblocks after a filesystem has already been created use [[newfs]] -N.

	Next (not counting the super-blocks) the filesystem is split into 2 parts. One ~~for a long index~~ (~~sequence of [[inode]]s~~) and the ~~other for~~ data. The inodes are the reference points for objects and data in the filesystem and they hold information such as:		Next (not counting the super-blocks) the filesystem is split into 2 different parts. One part is data and the other is meta-data(inodes). The way inodes are placed on the disk is original, the cylinders on the disk are placed in cylinder groups and each cylinder group holds inodes and data, inodes at the beginning of the cylinder group and data after. The inodes are the reference points for objects and data in the filesystem and they hold information such as:

	*[[permissions]]		*[[permissions]]
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	For more information on FFS see [http://www.cs.berkeley.edu/~brewer/cs262/FFS.pdf A fast filesystem for UNIX].		For more information on FFS see [http://www.cs.berkeley.edu/~brewer/cs262/FFS.pdf A fast filesystem for UNIX].



	== UFS2 ==		== UFS2 ==

Pbug: /* Magic Numbers */

2008-06-02T18:58:21Z

Magic Numbers

← Older revision		Revision as of 11:58, 2 June 2008
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	#define FS_UFS2_MAGIC 0x19540119 /* UFS fast filesystem magic number */		#define FS_UFS2_MAGIC 0x19540119 /* UFS fast filesystem magic number */

	We suspect these magic numbers are the ffs authors birthdays (in hex).		We suspect these magic numbers are the ffs authors birthdays (in hex). ;-)

Pbug: intro

2008-06-02T18:56:22Z

intro

← Older revision		Revision as of 11:56, 2 June 2008
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			== Intro ==

	The Berkeley FFS was written by Marshall Kirk McKusick for 4.2BSD at [[UCB]]. It resides on a disk [[partition]] in blocks greater or equal to 4096 bytes (no less). It has a super block that contains filesystem specific data (eg. when the last [[fsck]] took place, use dumpfs(8) to display the superblock, this is a very long listing) which is at block 0. It also has backup superblocks in case the first superblock is corrupted ([[fsck]] -b to repair a broken superblock and check the filesystem with an alternate superblock), the next superblock is at block 32 and the others are made known at [[newfs]] time.		The Berkeley FFS was written by Marshall Kirk McKusick for 4.2BSD at [[UCB]]. It resides on a disk [[partition]] in blocks greater or equal to 4096 bytes (no less). It has a super block that contains filesystem specific data (eg. when the last [[fsck]] took place, use dumpfs(8) to display the superblock, this is a very long listing) which is at block 0. It also has backup superblocks in case the first superblock is corrupted ([[fsck]] -b to repair a broken superblock and check the filesystem with an alternate superblock), the next superblock is at block 32 and the others are made known at [[newfs]] time.

Pbug at 18:55, 2 June 2008

2008-06-02T18:55:22Z

← Older revision		Revision as of 11:55, 2 June 2008
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	=== UFS2 ===		== UFS2 ==

	[[FreeBSD]] and [[NetBSD]] have a second version of FFS that allows [[filesystem]] sizes greater than 1 TB. This is UFS2. The size of an UFS2 inode is 256 bytes and thus UFS1 and UFS2 are not compatible.		[[FreeBSD]] and [[NetBSD]] have a second version of FFS that allows [[filesystem]] sizes greater than 1 TB. This is UFS2. The size of an UFS2 inode is 256 bytes and thus UFS1 and UFS2 are not compatible.


	=== Growing an FFS filesystem ===		== Growing an FFS filesystem ==

	If you happen to have a partition that doesn't use up the entire disk, it is possible to grow this filesystem. Before [[FreeBSD]] 4.4 this was not possible. Here is [[growfs\|the breakdown on how to grow an ffs filesystem]].		If you happen to have a partition that doesn't use up the entire disk, it is possible to grow this filesystem. Before [[FreeBSD]] 4.4 this was not possible. Here is [[growfs\|the breakdown on how to grow an ffs filesystem]].

	=== Soft Updates ===		== Soft Updates ==

	What are Soft Updates? A paper outlining its use and implementation is [http://www.usenix.org/publications/library/proceedings/usenix99/mckusick.html here].		What are Soft Updates? A paper outlining its use and implementation is [http://www.usenix.org/publications/library/proceedings/usenix99/mckusick.html here].
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	Side effects of having soft updates on the / filesystem are that a new kernel written to /bsd shortly before a panic will be corrupted requiring the next boot off a backup of the kernel.		Side effects of having soft updates on the / filesystem are that a new kernel written to /bsd shortly before a panic will be corrupted requiring the next boot off a backup of the kernel.

			== Magic Numbers ==

			In the file /usr/include/ufs/ffs/fs.h

			#define FS_MAGIC 0x011954 /* the fast filesystem magic number */
			#define FS_UFS1_MAGIC 0x011954 /* the fast filesystem magic number */
			#define FS_UFS2_MAGIC 0x19540119 /* UFS fast filesystem magic number */

			We suspect these magic numbers are the ffs authors birthdays (in hex).

Pbug: wording

2005-11-16T15:42:12Z

wording

← Older revision		Revision as of 08:42, 16 November 2005
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	*file group		*file group

	The data an inode holds is also called '''metadata'''. The size of a UFS1 inode is 128 bytes. By default an inode exists for every 8192 bytes of filesystem space, this is tweakable with [[newfs]] when the filesystem is ~~built~~.		The data an inode holds is also called '''metadata'''. The size of a UFS1 inode is 128 bytes. By default an inode exists for every 8192 bytes of filesystem space, this is tweakable with [[newfs]] when the filesystem is first created.

	[[Image:ffs.png]]		[[Image:ffs.png]]

Pbug: add reference to blocks of data in inode

2005-11-16T14:55:11Z

add reference to blocks of data in inode

← Older revision		Revision as of 07:55, 16 November 2005
Line 19:		Line 19:
	*[[mtime]]		*[[mtime]]
	*[[ctime]]		*[[ctime]]
	*disk blocks used by file		*references to blocks of data
			*number disk blocks used by file
	*chflags		*chflags
	*file owner		*file owner

Pbug: rearranging

2005-11-16T14:15:51Z

rearranging

@@ Line 11: / Line 11: @@
 Here in the example the backups are 32, 25032 and 50032.  To find out the alternate superblocks after a filesystem has already been created use [[newfs]] -N.
-Next (not counting the super-blocks) the filesystem is split into 2 parts.  One for a long index (sequence of [[inode]]s) and the other for data.  The inodes are the reference points for objects and data in the filesystem and they hold information such as [[permissions]], file link count, file size, [[atime]], [[mtime]], [[ctime]], disk blocks used by file, chflags, file owner and file group.  The data an inode holds is also called metadata.  The size of a UFS1 inode is 128 bytes.  By default an inode exists for every 8192 bytes of filesystem space, this is tweakable with [[newfs]] when the filesystem is built.
+Next (not counting the super-blocks) the filesystem is split into 2 parts.  One for a long index (sequence of [[inode]]s) and the other for data.  The inodes are the reference points for objects and data in the filesystem and they hold information such as:
 [[Image:ffs.png]]