Geom_Raid5 best practices ?

[Arnaud Houdelette]

I use geom_raid5 for my home NAS for  nearly 1 year.
No problems so far (but just the fact I had to patch ata-disk.c to 
modify the IO timeout in order to be able to use ataidle).

Since I updated to 7.0-RELEASE, I was wondering if I should use gjournal 
on the raid5 array.
The array's purpose is to store music (2-10 MB) and video (300MB to 8GB) 
files.

My system is as it follow :
- USB key for base system (power/sound efficient)
- 120 GB Pata disk  for temporary downloads, /usr/src, ports and obj
- 4x250 GB sata disks for mass storage (so 750GB usable space).

I currently use plain UFS+SU on every FS, and daily snapshots on the 
raid5 one.
GJournal should protect the raid5 UFS from destruction by bad power 
failures/kernel crashes, but with what performance impact ? Is the risk 
of complete FS crash really important with only SU ? (loss of data 
written at the time of the crash is no big deal, nor waiting for a fsck 
to complete, as long as I can recover most of the data previously stored)

But as the gjournal first introduction showed a big performance drop on 
big files (they apparently have to be written twice), I was really 
wondering if I should use a journal on the file system ?
If so, where should I put the journal on, and wich journal size should I 
use ?

Any advice ?