suggested block size for a frequently updated postgresql?

I'm planning on setting up a postgresql server, the database data
files are on their own slice so I can tune the file system for pgsql.

The database is pretty large. On my test server, some data files get
larger than 1G and is splitted by pgsql. Also the database will be
updated frequently.

I'm planning on setting the slice with a bigger block size/fragment
size but not sure if that's a good idea. I know the default on FreeBSD
is 16K/2K, I'm planning on something like 1M/128K.

The most concern is how the database files get updated? I heard that
most database do update/delete by appending a mark and new record at
the end of the data file but can't find any evidence for that. If
that's true, then the thing looks good. But if the database update the
data file by changing the original file block, setting a bigger block
size may bring extra effort for the drive, especially when it's a
RAID5 and a checksum build is required.

Can someone shine some light on this? Thanks!

-- 
Dryice @ http://dryice.3322.org

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