HP NetRaid performance problem

[Geoff Buckingham]

Is your performace equal on your RAID0 and RAID5 arrays?

If you see lesser performance on the RAID5 (which is likley), remember
the card has an XOR engine that may be over taxed, additioally remember, to
calculate that XOR the controller has to perform multiple reads to aquire the
bits to XOR.

The size of the stripe on the RAID 5 may have some impact although this is
a complex interaction between the physics of getting the drive heads to where
they need to be, limitations of the XOR engine and behavior of the filesystem,
particularly cluster size and where meta data gets stored on the array. (Tradition disk layouts on RAIDed voluems can lead to IO being concentrated on one spindle).

In short RIAD 5 ins't good for performance, particulary write performance. 
You may want to try a RAID1 configuration although you will obviously loose
disk space. With some applicatins you may see better perfomance with a software
RAID than some older controllers, allthough your data is probabley safer on
a hardware RAID.

You don't mention your application it may be significant.
You may be able to tune your application.

Dedicated servers from HP and others are often shipped with the write cache
on the SCSI disks disabled. This is the safest confiuration for your data.
However it is the slowest, particularley if your application waits on data
getting commited to the fs.

Your controller has 32MB RAM, do you know if this is used as a write cache?
It may require a rechargeable battery pack to be used as such. These are often
sold as an option (don't know if this is the case for HP NetRiad).
Obtaing battery and more RAM if you can expand the 32MB may help.(Again don't
know specifics of this card.)

If the amr driver makes individual spindles available as passX devices, you may be able to use camcontrol to alter the relevent scsi page to allow use of the
disks cache for writing. However you can do great harm to both your disk and
data with camcontrol *AND* the RAID 5 read to write requirement is far more 
likeley to be your problem. Even if you were to do this and get better 
performance your data would be less secure in this configuration. 



On Fri, Apr 09, 2004 at 03:44:38PM +0200, Miroslav Kes wrote:
> Hi,
> 
> I have HP NetServer  LH 3000 machine with the NetRAID controller ...
> 
> the dmesg says:
> 
> amr0: <LSILogic MegaRAID> mem 0xe0000000-0xefffffff irq 5 at device 3.1 
> on pci3
> amr0: <Integrated HP NetRAID (T7)> Firmware E.01.00, BIOS B.02.01, 32MB RAM
> 
> There is 1 disk (system) alone (RAID 0) and 3 disks (data) configured as 
> RAID 5 array. The problem is that the write performance is very poor  - 
> about 6 - 10 times slower than the read performance (with softupdates on).
> 
> Any idea what can be wrong would be really welcome.
> 
> Thanks
> 
> Mira
> 
> P.S. Unfortunately I'm currently loosing the battle with other (W2K 
> based) servers in hearts of my users in the office. Just because o that 
> problem.
> 
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