Re: write cache on 3ware controller and XFS

[Seth Mos <knuffie@xxxxxxxxx>]

At 20:50 5-11-2002 +0100, Christophe Zwecker wrote:
> Hi,
>
> I have write cache disabled on the 3ware controller. I copied 300 gb
> over network, I noticed that every 50mb or so, the controller stalled,
> didnt accept more data while writing like crazy to disk.

How much ram do you have in this server? Does the stall occur exactly every 
30 seconds == to time to fill ram?

> it took me 24 h to copy 300 gb over 100mbit network.

== ~3MB/s

With about the normal amount of maximum bandwidth of the 100Mbit interface 
it would take 10MB/sec => 8,5 hours

Maybe you could investigate Gigabit Ethernet and a cross over cable :-)
The 3ware controller should easily beat the 3MB/s mark though.

What disks are attached, what speed and size, how many, what sort of raid 
config. Does it have a battery cache.

>  After that I tried
> to turn write cache on, huge more performance. hmm well. I rebooted

Only turn on write caching if the thing has a batter cache to back up the 
ram in case of a power failure.

> couple of times, suddenley I could mount ther XFS partition any more
> (bad superblock). I disabled write cache again and thank god I could fix
> the issue with xfs_repair.

You were lucky :-/

> So, here I am , disbled write cache, ok. the performance as I stated
> above is awfull, is this how its supposed to be ? disable write cache
> and have terrible performance?

That sounds about right.

> also: Do I have to disable write cache on the drives themselfes too ?

Yes.

> I have another box with an SCSI ICP Controller and RAID5/XFS on it, I
> quickly disabled write cache there too, had it running for a year with
> (phew)  :-)

If it has a battery cache you are safe.

Cheers

--
Seth
It might just be your lucky day, if you only knew.