473,320 Members | 1,979 Online
Bytes | Software Development & Data Engineering Community
Post Job

Home Posts Topics Members FAQ

Join Bytes to post your question to a community of 473,320 software developers and data experts.

RAID 5 DISKS

Hi,
How do we count the total physical disks assigned to a DB2 database
on a RAID 5, solaris environment.

Thank you.

May 22 '07 #1
8 2178
vishnu wrote:
Hi,
How do we count the total physical disks assigned to a DB2 database
on a RAID 5, solaris environment.

Thank you.
Raid 5 = (n-1) DATA disk and PARITY disk. So if I have $aid5 array on 5
disk - I would consider that my DB2 has 4 Data disks.

Jan M. Nelken

May 22 '07 #2
vishnu wrote:
Hi,
How do we count the total physical disks assigned to a DB2 database
on a RAID 5, solaris environment.

Thank you.

I would consider this as:

Raid 5 on n disks = (n-1) DATA disk and PARITY disk.

So if I have $aid5 array on 5 disk - I would consider that my DB2 has 4
Data disks. OI know that parity chunk alternates between all disks - but
1 logical i/o operation activates 4 writes of data + 1 write of parity.

Jan M. Nelken

May 22 '07 #3
What cmd do I run to check the number of disks I have.

Jan M. Nelken wrote:
>Hi,
How do we count the total physical disks assigned to a DB2 database
on a RAID 5, solaris environment.

Thank you.

I would consider this as:

Raid 5 on n disks = (n-1) DATA disk and PARITY disk.

So if I have $aid5 array on 5 disk - I would consider that my DB2 has 4
Data disks. OI know that parity chunk alternates between all disks - but
1 logical i/o operation activates 4 writes of data + 1 write of parity.

Jan M. Nelken
May 22 '07 #4
On May 22, 10:27 am, "vishnu" <u34415@uwewrote:
What cmd do I run to check the number of disks I have.

Jan M. Nelken wrote:
Hi,
How do we count the total physical disks assigned to a DB2 database
on a RAID 5, solaris environment.
Thank you.
I would consider this as:
Raid 5 on n disks = (n-1) DATA disk and PARITY disk.
So if I have $aid5 array on 5 disk - I would consider that my DB2 has 4
Data disks. OI know that parity chunk alternates between all disks - but
1 logical i/o operation activates 4 writes of data + 1 write of parity.
Jan M. Nelken- Hide quoted text -

- Show quoted text -
For most purposes in DB2, a single arrary of 5 disks (or any number of
disks in the array) should be considered by a DBA to be one large
physical disk. But it may depend on why you asking the question.

May 26 '07 #5
Mark A wrote:
For most purposes in DB2, a single arrary of 5 disks (or any number of
disks in the array) should be considered by a DBA to be one large
physical disk. But it may depend on why you asking the question.
Right - for almost all purposes DB2 should be told that there is one
disk there.

But - sometimes it is beneficial to know number of data disks in array -
as well as physical raid stripe size - in order to calculate efficient
extend size and/or prefetch size.

Jan M. Nelken
May 26 '07 #6
On May 25, 9:58 pm, "Jan M. Nelken" <Unknown.U...@Invalid.Domain>
wrote:
Mark A wrote:
For most purposes in DB2, a single arrary of 5 disks (or any number of
disks in the array) should be considered by a DBA to be one large
physical disk. But it may depend on why you asking the question.

Right - for almost all purposes DB2 should be told that there is one
disk there.

But - sometimes it is beneficial to know number of data disks in array -
as well as physical raid stripe size - in order to calculate efficient
extend size and/or prefetch size.

Jan M. Nelken
Any time you are dealing with striped disks, the extent size should be
an even multiple of stripe size.

But for purposes of prefetch size, a single array should be considered
as one disk. When creating containers, if you follow the rule that for
a given tablespace there should only be one container per physical
disk, then if you have a single striped array of 5 disks, you should
consider that to be one disk. Since the prefetch size should be the
extent size, times the number of containers in the tablespace, then
the extent size would equal the prefetch size if only one array is
used (and one container is created for that tablespace in the single
array).

May 26 '07 #7
Mark A wrote:
Any time you are dealing with striped disks, the extent size should be
an even multiple of stripe size.

But for purposes of prefetch size, a single array should be considered
as one disk. When creating containers, if you follow the rule that for
a given tablespace there should only be one container per physical
disk, then if you have a single striped array of 5 disks, you should
consider that to be one disk. Since the prefetch size should be the
extent size, times the number of containers in the tablespace, then
the extent size would equal the prefetch size if only one array is
used (and one container is created for that tablespace in the single
array).
Setting extend size = prefetch size for that case you described above
would turn off prefetching, wouldn't it?

Jan M. Nelken

May 26 '07 #8
On May 26, 11:01 am, "Jan M. Nelken" <Unknown.U...@Invalid.Domain>
wrote:
Setting extend size = prefetch size for that case you described above
would turn off prefetching, wouldn't it?

Jan M. Nelken
Prefetch takes place when DB2 decides to put pages into the bufferpool
asynchronously before the pages are actually needed by DB2. In that
sense itt is based on an artificial intellignece algorithm. This
typically happens in a table scan of a large table where DB2 knows
that all the pages of the table will eventually need to be in the
bufferpool. But DB2 needs to make sure that prefetching is not too
fast if the bufferpool does not have room for all the pages, otherwise
previously prefetched pages could be flushed out before they are
actually used for the query.

Prefetching can certainly happen if prefetch size equals extent size.
DB2 will just prefetch one extent at a time (assuming that prefetch is
turned on and DB2 thinks it is a good idea for a specific query). The
reason for making the prefetch size equal to the extent size times
number of containers is that otherwise you will have disk contention
if you are prefetchng multiple extents from the same disk or array at
the same time. That is why you should generally only use multiple
containers if they can be placed on different disks or different
arrays.

May 26 '07 #9

This thread has been closed and replies have been disabled. Please start a new discussion.

Similar topics

6
by: Bernie | last post by:
I will be doing some performance testing on financial application next month. Without going into a lot of details, I suspect I will have a potential bottleneck when writing to the log file. My...
5
by: Mark Kirkwood | last post by:
Dear all, Here is the first installment concerning ATA disks and RAID controller use in a database server. I happened to have a Solaris system to myself this week, so took the opportunity to use...
8
by: Joseph | last post by:
I've been thinking about the benefits or lack thereof of deploying DMS tablespaces for RAID, say RAID 5. The point of DMS is to get reasonable size extents of contiguous disk space so that minimal...
4
by: esmith2112 | last post by:
We replaced an aging system with a newer (faster 4-way) and presumably better system. Perfomance for most queries has improved as one would expect. However, we're getting slaughtered on performance...
2
by: p175 | last post by:
Hi folks, I've tried reading just about every post I can on raid stiping / extent size etc and I'm just getting myself more confused than ever. Here's my situation. On a Windows Server 2000...
13
by: Dave | last post by:
RAID 5 beats RAID 10 Can I get some feedback on these results? We were having some serious IO issues according to PerfMon so I really pushed for RAID 10. The results are not what I expected. ...
17
by: boa | last post by:
I'm currently planning disk layouts and use for a new version of our database. The current version has all data and indexes in the default filegroup, placed on one big raid-5 array(6 drives) along...
110
by: alf | last post by:
Hi, is it possible that due to OS crash or mysql itself crash or some e.g. SCSI failure to lose all the data stored in the table (let's say million of 1KB rows). In other words what is the worst...
7
by: Scav | last post by:
Helpful folks, I am trying to find any doc or research or studies comparing the pros and cons of architecting a DB2 disk subsystem to physically segragate index access and data access on...
0
by: ryjfgjl | last post by:
ExcelToDatabase: batch import excel into database automatically...
0
isladogs
by: isladogs | last post by:
The next Access Europe meeting will be on Wednesday 6 Mar 2024 starting at 18:00 UK time (6PM UTC) and finishing at about 19:15 (7.15PM). In this month's session, we are pleased to welcome back...
1
isladogs
by: isladogs | last post by:
The next Access Europe meeting will be on Wednesday 6 Mar 2024 starting at 18:00 UK time (6PM UTC) and finishing at about 19:15 (7.15PM). In this month's session, we are pleased to welcome back...
0
by: Vimpel783 | last post by:
Hello! Guys, I found this code on the Internet, but I need to modify it a little. It works well, the problem is this: Data is sent from only one cell, in this case B5, but it is necessary that data...
1
by: PapaRatzi | last post by:
Hello, I am teaching myself MS Access forms design and Visual Basic. I've created a table to capture a list of Top 30 singles and forms to capture new entries. The final step is a form (unbound)...
0
by: CloudSolutions | last post by:
Introduction: For many beginners and individual users, requiring a credit card and email registration may pose a barrier when starting to use cloud servers. However, some cloud server providers now...
0
by: Defcon1945 | last post by:
I'm trying to learn Python using Pycharm but import shutil doesn't work
1
by: Shællîpôpï 09 | last post by:
If u are using a keypad phone, how do u turn on JavaScript, to access features like WhatsApp, Facebook, Instagram....
0
by: af34tf | last post by:
Hi Guys, I have a domain whose name is BytesLimited.com, and I want to sell it. Does anyone know about platforms that allow me to list my domain in auction for free. Thank you

By using Bytes.com and it's services, you agree to our Privacy Policy and Terms of Use.

To disable or enable advertisements and analytics tracking please visit the manage ads & tracking page.