external raid arrays

[Jakob Østergaard]

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).

-- 
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:.........................: putrid forms of man                :
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