[Beowulf] RAID for home beowulf

[Tomislav Maric]

First of all: thank you very much for the advice, Skylar. :)

So, all I need to do is to create the same partitions on three disks and
set up a RAID 5 on /home since I'll be doing CFD simulations (long
sequential writes) and use RAID 1 for other (system) partitions, to
account for recovery of the system in case of disk failure because log
writes are sequential and small in volume. I was reading about RAID 0,
but I'm not sure how safe is to use it for storing computed data and how
much speed would I get compared to RAID 5.

Sorry for the totally newbish questions.

I'm using Ubuntu, and after I install it, I'll try to configure the RAID
manually. How do I make sure that the boot loader is on all disks? I
mean, isn't RAID going to make the OS look at the /boot partition that's
spread over 3 HDDs as a single mount point?

Best regards,
Tomislav


Skylar Thompson wrote:
> Tomislav Maric wrote:
>> Hi everyone,
>>
>> I've finally gathered all the hardware I need for my home beowulf. I'm
>> thinking of setting up RAID 5 for the /home partition (that's where my
>> simulation data will be and RAID 1 for the system / partitions without
>> the /boot.
>>
>> 1) Does this sound reasonable?
>>   
> It depends on your workload. RAID5 is good for large sequential writes,
> but sucks at small sequential writes because for every write it has to
> do a read to compare parity.
> 
>> 2) I want to put the /home at the beginning of the disks go get faster
>> write/seek speeds, if the partitions are the same, software RAID doesn't
>> care where they are?
>>   
> 
> I don't think this will buy you much performance. There probably is a
> measurable difference, but I don't think it's enough to worry about.
> 
>> 3) I'll leave the /boot partition on one of the 3 disks and it will NOT
>> be included in the RAID array, is this ok?
>>   
> 
> Sure, but /boot is actually trivial to mirror. Just make sure your boot
> loader is on each disk in the mirror and that each disk is partitioned
> identically, and all you have to do if a drive dies is change the device
> you boot off of if a drive dies.
> 
>> 4) I've read about setting up parallel swaping via priority given to
>> swap partitions in fstab, but also how it would be ok to create RAID 1
>> array of swap partitions for the HA of the cluster. What should I choose?
>>   
> 
> Any swapping at all will kill performance. I would get enough RAM to
> make sure you don't swap.
> 
>> I've gone through all the software raid how-tos, FAQs and similar, but
>> they are not quite new (date at least 3 years) and there's no reference
>> to clusters. Any pointers regarding this?
> 
> If you're using a Red Hat-based distro, kickstart can handle software
> RAID. I don't know about other distros though.
>