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Old 12-04-2008, 08:02 AM   #1
iggi
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Registered: Nov 2007
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SMP kernel, hardware RAID


Hello,

I've 2 questions, one concerns SMP on Redhat Enterprise Linux 5. I had a VM with RHEL5 which had just one virtual processor. In GRUB there's only one entry which points to a regular (non-smp) kernel. Yesterdag I added an additional processor (VMware Workstation 6.5) and guess what, it just works (e.g. top, pressing '1' shows 2 CPUs which I can both load up to 100%). I don't understand... maybe there's no difference anymore in packages with/without SMP --> I cannot find a kernel-smp related RPM. On the other hand I know if you install RHEL on a dual processor system, it adds an SMP entry to GRUB (idem vmlinuz file I think)

2nd question concerns HW RAID on my physical system. On Fedora 9 and using Intel ICH9 hardware raid, all my raid volumes (e.g. existing Windows NTFS filesystems) are made available through /dev/mapper/... device files (per partition one device file). If I boot the Knoppix distro, it just creates /dev/sda[1,2,3...] devices which is what I expected in the first place. Why is this different? I don't want a device mapper file for each partition!

Thanks, I'm curious about the answers!!

Dirk
 
Old 12-04-2008, 08:38 AM   #2
farslayer
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ICH9 is not true Hardware RAID.. it is fakeRAID.
Linux dmraid has support for Intel Software RAID.

If you want true hardware RAID you need to look elsewhere - 3Ware, LSI, etc..
 
Old 12-04-2008, 09:21 AM   #3
iggi
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Looks like Redhat ships only 1 kernel which has SMP enabled by default. Can someone confirm? Some distributions ship with both and allow to select one a boot time.... not here.

As the RAID is concerned: yes, I know it's not TRUE hardware RAID but as far as I know there should be some hardware acceleration ?! Otherwise why add support to the chipset if you do it ALL in software... Question remains why knoppix behaves differently.
 
Old 12-04-2008, 10:27 AM   #4
farslayer
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Well the acceleration will come in exchange for Load on the CPU. The advantage of true hardware RAID is it takes care of that load on the controller itself with very little load on the CPU. I believe the linux Software RAID performs about equally to the Intel ICH9 RAID in terms of performance.

Quite frankly I have never understood the purpose of FakeRAID systems, they really seem to have ZERO advantages and several disadvantages.


I still can't answer your Knoppix question though.
 
Old 12-04-2008, 10:50 AM   #5
Quakeboy02
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Quote:
Originally Posted by farslayer View Post
Quite frankly I have never understood the purpose of FakeRAID systems, they really seem to have ZERO advantages and several disadvantages.
The fakeraids are there to give you the raid while the system is booting up, but before the host OS takes over. The advantage is that you can put your OS on the fakeraid and have it mirrored or striped. The disadvantage is that all maintenance functions must be done in the BIOS, and are thus limited to the features in the BIOS.
 
Old 12-04-2008, 12:50 PM   #6
iggi
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Thanks both! On another PC I have an Adaptec RAID controller with lots of cache, and indeed it rocks!! But still: the "software" RAID is not that bad... it's cheap and big file transfers are considerably faster.
 
  


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