20TB Storage System (fsck????)

[Chuck Swiger]

Max Clark wrote:
> Ohh, that's an interesting snag. I was under the impression that 5.x w/ PAE
> could address more than 4GB of Ram.

It can.  PAE lets the hardware address more than 4GB of RAM, but that doesn't 
change how much memory you can give to any one process: a 32-bit process still 
has a 32-bit virtual address space.

> If fsck requires 700K for each 1GB of Disk, we are talking about 7GB of Ram
> for 10TB of disk. Is this correct? Will PAE not function correctly to give
> me 8GB of Ram? To check 10TB of disk?

Another thread suggests that the maximum amount of memory actually available for 
a 32-bit process to use under FreeBSD is a little less than 3 GB.

> Is there anyway to bypass this requirement and split fsck into smaller
> chunks? Being able to fsck my disk is kinda important.

Sure.  Create multiple filesystems rather than just one, and use symlinks to 
make the directory namespace fit your needs.

I don't know enough about your tasks to give you really specific advice, but I'm 
wary of the write-performance hit from putting too many drives wide in a RAID-5 
(or -5,0) configuration.  If you can split up your data by role or typical 
access pattern, you might well be able to identify some chunks that will be 
read-mostly (and RAID-5,0 is a good fit) and others that will be read-write or 
even write-mostly (and thus should be on -1,0).  You can also tune other things 
like blocksize, # of inodes, and so forth more appropriately for each filesystem.

-- 
-Chuck