The notion of an extant is that it can grow upto apt where it doesn't reach another extant on disk. Its extensible till space permits, and unlike a disk block which can be of 4096/8192 bytes etc. That explains why you see only 1 extant having internal fragmentation. You should see some more fragmentation if the disk is heavily used up in terms of adding/deketing files upto max capacity of disk. If your boss doesn't like JFS, you can use other extant based filesystems like VxFS.
regards -kamal On 7/10/06, Cosmo Nova <[EMAIL PROTECTED]> wrote: > > Hi, > > I am working on a digital video recorder. The system is linux based and > there are 16 video sources. The video sources write data the data disk > syncronously. Once it is filled up, there is a recycle mechanism which will > remove the old video files and free up new space. As you can imagined, there > will be serious external fragmentation problem as time passes. > I was told that jfs and xfs can do much better than ext3, to tackle the > fragment problem, so I conducted a few benchmark tests and found that jfs is > doing excellent job. The findings is not strong enough to persuade my boss > to change, and hence I've been reading the rationale and source code behind > jfs. Here I summarized two major questions that can help me explain jfs's > magic: > > 1. when I write the first byte or open a file, what will jfs do? cuz my > findings is that, the 16 channels create files of size around 32MB. They > grow in size of course, but majority fragment or number of extents I found > is only ONE... > > according to ur disscussion with Peter, jfs allocates one page to a file at > a time. and this allocation is locked under one allocation group. the page > size according to jfs_filesys.h is 4096. You said the allocation would be > allocated but not recorded (ABNR), which raised two subquestions: > 1a. is those ABNR blocks stored temporary in memory, 16 files on grow and > towards 32MB, it is a huge memory requirement. is it really that everyone > stored in memory and flushed to the disk at file close?? what is the jfs > memory requirement then? > 1b. since only one file is allocated in one allocation group (AG), then how > many AG is there in ur disk when it's formated (mkfs)? and is there an upper > bound for the maximum number of files which can be opened and written at the > same moment in jfs?? > > 2. jfs is so called extent-based allocation. how jfs knows the right size of > extent to allocate to a fixed file? and growing file? the stat i found shows > that majority of my files ( <= 32MB ) are single fragment file (number of > extent = 1). I would really like to understand the "magic" how it can be > achieved. > > The findings and rationale behind will lead us to a filesystem change. I > would be very gladful if anyone can help me. Thankyou very much! > -- > View this message in context: > http://www.nabble.com/Some-more-questions%2C-preallocation-tf440979.html#a5247869 > Sent from the JFS - General forum at Nabble.com. > > > > ------------------------------------------------------------------------- > Using Tomcat but need to do more? Need to support web services, security? > Get stuff done quickly with pre-integrated technology to make your job > easier > Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo > http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 > _______________________________________________ > Jfs-discussion mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/jfs-discussion > ------------------------------------------------------------------------- Using Tomcat but need to do more? Need to support web services, security? Get stuff done quickly with pre-integrated technology to make your job easier Download IBM WebSphere Application Server v.1.0.1 based on Apache Geronimo http://sel.as-us.falkag.net/sel?cmd=lnk&kid=120709&bid=263057&dat=121642 _______________________________________________ Jfs-discussion mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/jfs-discussion
