Slower performance with ext4

[Mark Kirkwood]

Christopher Chan wrote:
>
>
> Yawn. Been there and done that. Without bbu cached hardware raid. Just 
> plain Linux software raid. XFS = pray for no power loss and ext3 
> data=journal  =  sleep well at night (except for spammers getting 
> through the developers' webmail system).
>
>
> You are using hardware raid + bbu and you have no need to delve deep 
> into how the filesystems work. If you do not want to take even the 
> standard explanations for ext3's (which are repeated for ext4) different 
> journaling modes then that is just too bad. Just stop propagating the 
> myth that fsync = return after data has been written to the filesytem. 
> If that was the case, there would not be large differences in filesystem 
> performance
>
>   
Double yawn - of course there is a *performance* difference - different 
filesystems do writes different ways (extent vs not for instance), 
however reliability is determined by the interaction with the device 
layers write cache (amongst other things - but that is the main effect 
here). Not matter how clever the filesystem - if the underlying hardware 
does not actually do the writes as requested (queue cheap sata as I've 
mentioned), then all bets are off. Hence the market for battery backed 
raid controllers for sata drives in particular (and note that these are 
worth using particularly 3Ware and Areca).

So to reiterate - guaranteeing writes to filesystem is good - but not 
good enough if the underlying device does not honor the software 
request. This is the guts of most workstation corruption problems, 
regardless of fs type.

For instance, I have experienced power interruption data loss on my 
workstation (ext3 filesystem + cheap sata drive) - and this is expected 
from this type of hardware.

regards

Mark