[Bioclusters] A set of notes on how to do RAID optimization on a compute node

[Allen Day]

Joe,

Have you had any experience setting up a RAID with one of the IDE 
RAID controllers?  I'm considering setting up a RAID 0, and want to know 
if I can benefit from using one of these controllers rather than just 
putting in an ATA card.

-Allen

On Mon, 12 Aug 2002, Joe Landman wrote:

> Hi Simon:
> 
> On Mon, 12 Aug 2002, Vsevolod Ilyushchenko wrote:
> 
> > Joe,
> > 
> > This is a very informative article. Thank you. A couple of followup 
> > questions:
> > 
> > 1. How would I do a software raid with more than two disks. That is, 
> > what PC hardware configuration to have more than two independent 
> > controllers. The only way to get them that I know of is through a RAID 
> > card, but the card will be the bottleneck then.
> 
> The PCI bus will be your limiting factor for IDE.  If you build a SCSI 
> based system, using Ultra 160 SCSI on a PCI-66 (266 MB/s bus), you 
> normally would achive about 200 MB/s sustainable bandwidth (the budget you 
> have to work with).  If each disk can talk at 40 MB/s (10k RPM disks can 
> do this), then you can in theory have 5 disks in a RAID0 stripe (just add 
> more 
> 
> 	device	    /dev/disk
> 	raid-disk     N+1
> 
> lines in your /etc/raidtab.  The /dev/disk is the disk device, and the N+1 
> is the next raid disk number (starting from 0).  So if you have 5 scsi 
> disks, sda to sde, all using partition 2 for the file system, your 
> /etc/raidtab file would have the device section looking more like this:
> 
>         device      /dev/sda2
>         raid-disk   0
>         device      /dev/sdb2
>         raid-disk   1    
>         device      /dev/sdc2
>         raid-disk   2    
>         device      /dev/sdd2
>         raid-disk   3    
>         device      /dev/sde2
>         raid-disk   4    
> 
> Of course, your chunk-size parameter will need to be optimized, and you 
> will need to change the nr-raid-disks to 5.
> 
> This will give you RAID0, 5 way striping.
> 
> For IDE, you can purchase an inexpensive ATA100 IDE card for PCI, and put 
> 2 disks on it (one on each channel).  Together with another disk on the 
> main IDE channels, you can get a 3 way stripe, which should put you pretty 
> close to 100 MB/s.
> 
> > 2. In general, how much of a speedup do you expect if you use 2-disk and 
> > 5-disk software raid, compared to the same disk drive used standalone?
> 
> Raither hard to answer a general question like this:  Which version of 
> RAID ... RAID 0?  1, 3, 5?  Which file system, what type of access pattern 
> (large sequential block reads, versus smaller random reads and writes).
> 
> This quickly gets into a discussion of how to tune for a specific range of 
> applications.  My company, Scalable Informatics (formed after I left 
> MSC.Software), could help answer some of these.
> 
> Let me know if you want to talk.  Thanks Simon!
> 
> Joe
> 
> > 
> > Thanks,
> > Simon
> > 
> > Joe Landman wrote:
> > > Hi folks:
> > > 
> > >   Chris had asked about methods to to RAID optimization on compute
> > > nodes.  The idea being that he could get good/better performance out of
> > > his system if he tuned various options in the software RAID0 under
> > > linux.
> > > 
> > >   The following URL is a short writeup I had been working on for a while
> > > now.  
> > > 
> > > http://scientificappliance.com/scalable_fs_part_1.html
> > > 
> > > If you have any questions or comments, please feel free to send them to
> > > me.   Thanks!
> > > 
> > 
> > 
> > 
> 
>