Since the controller must
calculate the parity data every time a write is done, there is a decrease on
performance when compared with reads, which doesn’t require the parity
calculation. On a RAID_10, there is no parity calculation on either read or
write, but there’s almost always a small slowdown in the write performance,
due to the disk internals. This means that a RAID_10 has faster read and write
speeds, over a RAID_5, the difference is depending upon the computing capacity
of the controller: In a FAStT900 should be less noticeable than in a FAStT200,
with a much smaller processor and cache.
HC
From:
IBM AIX Discussion List
[mailto:aix-l@xxxxxxxxxxxxx] On Behalf Of Vincent
D'Antonio
Sent: Wednesday, January 11, 2006
4:10 PM
To: aix-l@xxxxxxxxxxxxx
Subject: Re: AIX V5.3 &
FASTT500 PERFORMANCE TUNING
I think this is backwards, raid5 should be better at writes and raid10
is better at reads.
There are number of different RAID levels see below some info that
might help you choose what is best for you:
· Level 0 -- Striped Disk Array without Fault Tolerance:
Provides data striping
(spreading out blocks of each file across multiple disk drives) but
no redundancy. This improves performance but does not deliver fault tolerance.
If one drive fails then all data in the array is lost.
· Level 1 -- Mirroring and Duplexing:
Provides disk
mirroring. Level 1 provides twice the read transaction rate of single disks
and the same write transaction rate as single disks.
· Level 2 -- Error-Correcting Coding: Not a
typical implementation and rarely used, Level 2 stripes data at the bit level
rather than the block level.
· Level 3 -- Bit-Interleaved Parity: Provides
byte-level striping with a dedicated parity disk. Level 3, which cannot service
simultaneous multiple requests, also is rarely used.
· Level 4 -- Dedicated Parity Drive: A
commonly used implementation of RAID, Level 4 provides block-level striping
(like Level 0) with a parity disk. If a data disk fails, the parity data is
used to create a replacement disk. A disadvantage to Level 4 is that the parity
disk can create write bottlenecks.
· Level 5 -- Block Interleaved Distributed Parity:
Provides data striping at the byte level and also stripe error correction
information. This results in excellent performance and good fault tolerance.
Level 5 is one of the most popular implementations of RAID.
· Level 6 -- Independent Data Disks with Double Parity:
Provides block-level striping with parity data distributed across all disks.
· Level 0+1 – A Mirror of Stripes: Not
one of the original RAID levels, two RAID 0 stripes are created, and a RAID 1
mirror is created over them. Used for both replicating and sharing data among
disks.
· Level 10 – A Stripe of Mirrors: Not
one of the original RAID levels, multiple RAID 1 mirrors are created, and a
RAID 0 stripe is created over these.
· Level 7: A trademark of Storage Computer
Corporation that adds caching to Levels 3 or 4.
· RAID S: EMC Corporation's proprietary
striped parity RAID system used in its Symmetrix storage systems.
On 1/11/06, Hernán
Camargo <hercom@xxxxxxxxxx>
wrote:
No data of a production database should be in a
RAID0. Multiply the chance of failure of each disk * the number of disks.
RAID_0 is useful ONLY in environments in which the data can be restored easily,
and the speed is over the availability (video capture, benchmarking, and
development).
Better:
- Check the behavior
of your applications in terms of reads/writes
- Calculate the amount
of space needed for your application
- Calculate the amount
of space needed to grow your application up to your next IT renovation
- Calculate the number
of I/O transactions per second desired. Then calculate the capacity the
array will have (50 TPS per disk is a good start)
Then:
- If your database is
mostly read-intense, RAID_5 will give you great performance and more space
to use.
- If your database is
write-intense, and you can afford it, use RAID_10, otherwise, use RAID_5.
Only use RAID_0 if you don´t care about loosing your data.
- Sometimes, two
arrays (and two LUNS) can give you better performance, if the indexes and
data are separated, or if two very active tablespaces are separated. There
is no improvement if the two LUNs are on the same RAID on the FAStT.
- The most of the
tuning should be made at database level. Assign a generous amount to the
buffers if you fell you have an I/O bottleneck. Remenber to use vmtune or
it's equivalents to reduce (in a great amount) the memory available to
filesystem cache, since most modern database engines use it's own method
to cache data, and do it on the memory allocated for the engine (eg. SGA).
- Adjust the
read-ahead paramenter in the FAStT, according to the expected behavior of
your database.
- Adjust the
read-ahead paramenter of AIX, according to the expected behavior of your
database.
- There´s a lot to
tunning in the process area, dedicated vs. shared an so on… out of
the scope of this thread.
HC
From: IBM AIX Discussion List [mailto:aix-l@xxxxxxxxxxxxx] On Behalf Of Alexandre Sato
Sent: Tuesday, January 10, 2006
6:04 PM
To: aix-l@xxxxxxxxxxxxx
Subject: Re: AIX V5.3 &
FASTT500 PERFORMANCE TUNING
I would consider to change the RAID 5 configuration for a RAID 0 or
RAID0 +1
RAID5:
-
Suitable for OLTP databases that do most reads in large blocks of data.
-
Suitable for Historical databases
- Do
unnecessary I/O to preserve parity check
RAID0:
- Data
spread around spindles. So I/O also.
-
Suitable for high intensive I/O, such OLAP databases.
-
Adding disk mirroring (RAID0+1) would increase high availability, but it costs
more disks.
I
sugest this redbook also:
http://publib-b.boulder.ibm.com/Redbooks.nsf/RedbookAbstracts/SG245511.html
Best
Regards!
Alexandre.
Hi
fellow AIX friends & associates:
I have a problem that I need your help with
concerning a FAStT500 (3552-1RU)
directly connected (not connected through a
switch) to an 8-way RS/6000
Model M80 with 16384MB of ram running AIX V5.3
ML03 (with post-ML03 fixes).
The M80 described above is being used for DB2 OLAP
V8.2 testing. The
firmware on both the M80 and the FAStT500 is
up-to-date. There are two (2)
EMULEX LP9002L cards installed in the M80 with
data fibre channel cables
connected from each LP9002L to the FAStT500
storage controller.
There is a 1TB RAID-5 LUN presented to AIX, and
cfgmgr shows the LUN as
hdisk5. There is only one active controller
(being controller A) that
fget_config -A is reporting for dac0.
We are using Storage Manager V9.12 to manage and
configure the DASD on the
FAStT500.
We are hoping to see better write performance on
FAStT500 when our OLAP job
runs; the problem for me is: Where do I
begin with respect to tuning on AIX
as well as the FAStT500? I have done AIX
tuning in the past using AIX V4.x
on internal and external SSA, but I am at a loss
as to fibre channel, as
well as the FAStT500.
As for the current write performance when our OLAP
jobs runs: I can see a
maximum of 20MB/s with an average of 9MB/s.
However, when I run a "tar -cvf
. . . " on a filesystem that resides on the
FAStT500 I've seen as high as
78MB/s and an avg. of 42MB/s sustained.
Where do I start? Any pointers? I've
read as much as I can presently
absord concerning the FAStT500 as well as the new
AIX performance tuning
commands.
I will be most happy to supply more detailed
information upon request.
--
Best Regards, I Am,
Joseph Kremblas
Phone: (919) 484-3071
IBM Certified Advanced Technical Expert (CATE) -
RS/6000 (pSeries) AIX
IBM Certified Specialist - RS/6000 SP AND PSSP 3.1
IBM Certified Specialist - pSeries AIX V5.1
Systems Support
IBM Certified Specialist - pSeries AIX V5.1 System
Administration
IBM Certificate of Proficiency - AIX
Communications
IBM Certificate of Proficiency - AIX Installation,
Backup and System
Recovery
IBM Certificate of Proficiency - AIX Problem
Determination
IBM Certificate of Proficiency - AIX Performance
and Systems Tuning
IBM Certified Specialist - AIX V4.X Systems
Support
IBM Certified Solutions Expert - MQSeries
IBM Certified Specialist - MQSeries
"Doubt is a pain too lonely to know that
faith is his twin brother."
All Rights Reserved.
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