SSA RAID vs. LVM Strip width
char...@my-deja.com
internal drives and 24 SSA drives hooked up to an SSA RAID Controller.
I'm going over the stripe size requirements with the DBA for the
filesystems we will use for the database and I'm kind of stuck between
the SSA RAID 5 stuff and the LVM values. There is probably something I
don't understand.
My problem is if I create an 11 drives RAID disk, say hdisk10. Than I
create a volume group and a logical volume for my data with a stripe
size of 128k, where will LVM stripe. From an LVM perspective, all it
sees
is the hdisk10 (who is actually pdisk10 - pdisk21) so it won't be able
to stripe across all eleven drives.
On the other hand, if I use the SSA drives indepandently, than I can
make a clean 128k stripe across 11 SSA drives but I loose the RAID 5
functionality...
I'm a bit lost here. Thanks for tips, links or anything on creating
specificaly stripped LVM volumes on an SSA RAID drive.
Thanks.
Sent via Deja.com http://www.deja.com/
Before you buy.
Bruce Elrick
>
> We are trying to setup an Oracle database running on an S7A with 10
> internal drives and 24 SSA drives hooked up to an SSA RAID Controller.
>
> I'm going over the stripe size requirements with the DBA for the
> filesystems we will use for the database and I'm kind of stuck between
> the SSA RAID 5 stuff and the LVM values. There is probably something I
> don't understand.
>
> My problem is if I create an 11 drives RAID disk, say hdisk10. Than I
> create a volume group and a logical volume for my data with a stripe
> size of 128k, where will LVM stripe. From an LVM perspective, all it
> sees
> is the hdisk10 (who is actually pdisk10 - pdisk21) so it won't be able
> to stripe across all eleven drives.
The RAID does the striping across pdisk10-21. You don't need to do LVM
striping in that case. If RAID 5 does not perform well enough for you
(because of the parity overhead) then you need to consider alternatives.
The latest SSA RAID adapters do RAID 0, 0+1, 1, & 5 so you can always
go to RAID 0+1 for best performance and protection at the cost of more
disks (2N vs. N+1).
>
> On the other hand, if I use the SSA drives indepandently, than I can
> make a clean 128k stripe across 11 SSA drives but I loose the RAID 5
> functionality...
>
> I'm a bit lost here. Thanks for tips, links or anything on creating
> specificaly stripped LVM volumes on an SSA RAID drive.
>
Someone can correct me if I'm wrong, but when you create a RAID set
you can choose the hardware striping size; you could try a number of
sizes to see which is best.
Cheers...
Bruce
--
Bruce Elrick, Ph.D. Saltus Technology Consulting Group
Personal: bel...@home.com IBM Certified Specialist
Business: bel...@saltus.ab.ca ADSM, AIX Support, RS/6000 SP, HACMP
Steve Harris
some other considerations.
If you are going to be using the parallel query facilities of oracle,
you need to put your tablespaces over multiple disks.
Oracle chooses degree of parallelism based on number of CPUs and number
of disks over which the data is spread.
Certainly, a single Large RAID drive will limit your options as Oracle
thinks this is one large disk.
If you really must go RAID and can afford the disk, consider several
smaller raid sets e.g. 4 drives each.
Regards
Steve Harris
AIX/ADSM/Oracle/HACMP Guy
The Wesley Hospital, Brisbane Australia
char...@my-deja.com wrote:
> We are trying to setup an Oracle database running on an S7A with 10
> internal drives and 24 SSA drives hooked up to an SSA RAID Controller.
>
> I'm going over the stripe size requirements with the DBA for the
> filesystems we will use for the database and I'm kind of stuck between
> the SSA RAID 5 stuff and the LVM values. There is probably something I
> don't understand.
>
> My problem is if I create an 11 drives RAID disk, say hdisk10. Than I
> create a volume group and a logical volume for my data with a stripe
> size of 128k, where will LVM stripe. From an LVM perspective, all it
> sees
> is the hdisk10 (who is actually pdisk10 - pdisk21) so it won't be able
> to stripe across all eleven drives.
>
> On the other hand, if I use the SSA drives indepandently, than I can
> make a clean 128k stripe across 11 SSA drives but I loose the RAID 5
> functionality...
>
> I'm a bit lost here. Thanks for tips, links or anything on creating
> specificaly stripped LVM volumes on an SSA RAID drive.
>
John Newman
I have done quite a bit of work in this area, and here are my
recommendations.
1. Use a strip size of 64K, hardware wise this is the most efficient.
2. From a software point of view you also need to tell the kernel that
it needs to read a minimum of 64K at a time. I believe that the norm is
16K, in doing this there are other setting that also need to be changed.
This is the setting that we use.
# -r 16 # min read ahead buffers
# -R 128 # max read ahead buffers
# -f 2048 # min free frames
# -F 4096 # max free frames
# -u 64 # up the RAW F/S buffers
# -p 5 -P 10 # Set MIN and MAX % of memory for caching files
/usr/samples/kernel/vmtune -r 16 -R 128 -f 2048 -F 4096 -u 64 -p 5 -P 10
Regards, John.
In article <89jenp$phr$1...@nnrp1.deja.com>,
Darrell Frappier
>We are trying to setup an Oracle database running on an S7A with 10
>internal drives and 24 SSA drives hooked up to an SSA RAID Controller.
>
>I'm going over the stripe size requirements with the DBA for the
>filesystems we will use for the database and I'm kind of stuck between
>the SSA RAID 5 stuff and the LVM values. There is probably something I
>don't understand.
>I'm a bit lost here. Thanks for tips, links or anything on creating
>specificaly stripped LVM volumes on an SSA RAID drive.
Take a look at one of the best IBM Redbooks I've seen lately: Database
Performance on AIX in DB2 UDB and Oracle Environments, SG24-5511-00
http://www.redbooks.ibm.com/pubs/pdfs/redbooks/sg245511.pdf
It gives very detailed and specific suggestions and has a good section
on SSA RAID performance. The book strongly suggests SSA write cache
card to have adequate write performance. My experience is that an SSA
memory feature is needed to use the full SSA write cache feature.
Darrell Frappier Detroit MI N3JWJ frap...@iname.com
Chuck Kuhlman
short of amazing. Properly set up, raid 0+1 is incredibly fast with
these cards.
Raid 5 is very very fast as well.
Using monitor and oracle performance tools, the write delay on these
cards is occasionally too low to measure.
seriously.
I do not put more than 32 drives per adapter loop. Always build your
raid 0+1 from 8 drive stripe sets, then mirror them.
With raid 5, go with 7+1 raid sets.