external raid arrays

Jakob Østergaard jakob at unthought.net
Thu Feb 21 18:04:20 EST 2002


On Thu, Feb 21, 2002 at 02:43:51PM -0600, Chris Black wrote:
> On Thu, Feb 21, 2002 at 10:53:43AM -0600, Chris Black wrote:
> > We are looking for an external RAID solution that will provide at LEAST 
> > 100MB/s read bandwidth, probably under RAID 10 (0+1). So far I have been 
> 
> This is a follow-up with more information that people asked for. Almost 
> all the I/O will be single process importing, exporting and doing 
> other operations on a MySQL database. The size we would like is around 
> .5TB. We currently use 3ware cards with 8 IDE disks using raid 0+1 and 
> get GREAT performance, but we are now looking for an external solution 
> with comparable bandwidth. Most companies either don't mention bandwidth 
> speeds at all, or just quote the maximum for the channel (e.g., 160MB/s 
> for Ultra160/Ultra3). The program we have been using to do benchmarks 
> is bonnie++.

Ok - 0.5T should be easily achievable with the simple external SCSI disk
solution.

Do you know that your workload is actually bandwidth limited and not seek-time
limited ?  You seem to focus on bandwidth, but I would imagine that most
database operations would be fairly insensitive to bandwidth since they would
spend most of their time waiting for the disks to seek....  Do you have
measurements ?

The RAID-1 support in the Linux kernel is pretty clever wrt. seeks/reads. You
could even consider adding more disks to your RAID-1 sets, not because of the
extra redundancy, but because of the improved seek times.   That is, if it
turns out that seek time is actually a limiting factor.  (What the linux kernel
will do is, to pick the disk with it's head positioned nearest to the position
where the next read is occurring - with RAID-1 this is possible).

-- 
................................................................
:   jakob at unthought.net   : And I see the elder races,         :
:.........................: putrid forms of man                :
:   Jakob Østergaard      : See him rise and claim the earth,  :
:        OZ9ABN           : his downfall is at hand.           :
:.........................:............{Konkhra}...............:
_______________________________________________
Beowulf mailing list, Beowulf at beowulf.org
To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf



More information about the Beowulf mailing list