[CentOS] Re: software raid
John R Pierce
pierce at hogranch.com
Thu Mar 29 18:44:44 UTC 2007
> 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.
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