[Beowulf] hardware RAID versus mdadm versus LVM-striping

Richard Chang rchang.lists at gmail.com
Tue Jan 19 11:44:59 EST 2010


Joe Landman wrote:
>
> Hi Richard:
>
>   This I cannot tell you, as I don't have a comprehensive list of what 
> uses what driver.  I'd suggest looking at what drivers it loads for 
> disks when it comes up.  If dmraid comes up *and* enumerates devices, 
> you have a strong probability that it is a fake-raid.  This is not to 
> say dmraid is bad.  Again, its the underlying driver or chipset that 
> we often run into problems with.
Thanks Joe,

This is a much better picture. I am sure there is no such thing as 
"dmraid" coming up when the system I maintain, starts.
>
>
> Rarely.  Fake raid will generally not have any RAM cache or battery 
> backup capability.

I am also sure, all the storage controllers that I have mentioned have a 
Battery and RAM Cache.

> In some instances, fake raid is *ok* for OS drives (RAID1 only), if 
> the bios is smart enough to use it correctly, the underlying fake raid 
> driver is relatively stable, and you have reasonable disks.  
> Otherwise, mdadm works great, though you have to patch Redhat/Centos, 
> as they, by default, use dmraid for the moment.  Later model Fedora 
> appear to have switched to MD raid (after 9 from what I saw, last time 
> I played with it).

I really appreciate your effort and the time taken to reply back.

Thanks,
Richard


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