[CentOS] Re: software raid

Thu Mar 29 18:44:44 UTC 2007
John R Pierce <pierce at hogranch.com>

> http://en.wikipedia.org/wiki/FAT32 claims 4GB filesize, and 8TB partition
> size. the 32GB partition limit is a WinXP-ism to make people use NTFS.

a 300 Gb fat32 would have either an obscenely large fat table, or an 
obscenely large cluster size.   if you used 4k clusters, each 'fat' 
table would be 300 megabytes, this has to be sequentially scanned to 
calcuate freespace, and it has to be scanned to find free blocks for 
file and directory allocations.    If you used 32k byte clusters, this 
would be reduced to 37 megabytes for the FAT, but then even the tiniest 
files would waste 32 k bytes.

FAT also has no support for file ownership or access rights.   It has no 
journaling, so any abnormal events such as unexpected/sudden reboots 
WILL result in lost freespace (orphaned files/fragments), AND its prone 
to crosslinking which is very hard to repair.    FAT was designed for 
floppy disks and hard disks that were a few megabytes back in the early 
80s.   It has no way of grouping cluster allocations together, so it has 
a very strong tendancy to extreme fragmentation, and as the FAT tables 
are quite large on a filesystem this size, requires frequent extra seeks 
to locate the next block.   4GB is an absolute limit on size of a single 
file (so, no DVD ISO images, no large TARs, etc).   Directories are 
sequentially scanned only, so large directories that spill over a few 
clusters become excruciatingly slow to even open files from.