Re: Squid & Advfs disks

On Fri, 14 Apr 2000, Ian Spare wrote:

]>You will definitely want to use advfs, as it is an extent-based filesystem
]>like VxFS, which will solve the fragmentation issues that you typically see on
]>a UFS filesystem. I suspect that as per your options with advfs, it probably
]
]I thought that UFS file systems only fragmented when allocated blocks
]in the last few percent of a disk while the allocation strategy of
]VxFS (which I take to be the standard name of Veritas File System)
]will fragment relatively quickly as it uses up the pools of large free
]extents. This is why I thought there were no defrag tools for UFS file
]systems (normally) and they're were for VxFS.

Hmm, what fragments are we talking about? UFS does store the last piece of
a file which does not fit into a block into special fragment blocks, if
the leftover piece is small enough. There is also the fragmentation of
keeping all blocks/sectors of a file in the neighbourhood of each other
(as opposed to spreading the file over the remaining free blocks on the
disk by the time free space has gotten thin). UFS (on Solaris) uses block
allocation (as opposed to extend based allocation), but still *tries* to
allocate sequential blocks.

With Solaris, I ran into one of those UFS fragmentation walls a few times,
until I limited cache_dir to 80% of the kbytes reported by "df -k". VxFS
is said to do things better, but I haven't got my hand on any VxFS (yet).
So far, it was cheaper to leave part of the disk unused (so that
fragmentation and sequential allocation algorithms can work) than to buy
VxFS.

Just because there is no defrag for UFS does not mean that there are no
fragments in UFS.

Le deagh dhùrachd,
Dipl.-Ing. Jens-S. Vöckler (voeckler@rvs.uni-hannover.de)
Institute for Computer Networks and Distributed Systems
University of Hanover, Germany; +49 511 762 4726
Received on Fri Apr 14 2000 - 02:35:23 MDT