external raid arrays
Jakob Østergaard
jakob at unthought.net
Thu Feb 21 15:04:20 PST 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}...............:
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