Horton

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  1. Hardware performance

    Balazs Wellisch <balazs@neusolutions.com> — 2003-07-17T02:57:22Z

    Hi all,

first of all I'd like to thank everyone who responded to my earlier post. I have a much better understanding of postgres performance tuning now. In case anyone's interested we've decided to go with RH9 and PostgreSQL 7.3 and we'll do the OS and DB tuning ourselves. (should be a good learning experience)

We are now getting ready to purchase the hardware that will be used to run the database server. We're spending quite a bit of money on it because this will eventually, if things go well within two months, become a production server. We're getting all RH certified hardware from Dell. (Dell 2650)

We're now stuck on the question of what type of RAID configuration to use for this server. RAID 5 offers the best fault tolerance but doesn't perform all that well. RAID 10 offers much better performance, but no hot swap. Or should we not use RAID at all. I know that ideally the log (WAL) files should reside on a separate disk from the rest of the DB. Should we use 4 separate drives instead? One for the OS, one for data, one for WAL, one for swap? Or RAID 10 for everything plus 1 drive for WAL? Or RAID 5 for everything?

We have the budget for 5 drives. Does anyone have any real world experience with what hard drive configuration works best for postgres? This is going to be a dedicated DB server. There are going to be a large number of transactions being written to the database. (Information is logged from a separate app through ODBC to postgres) And there will be some moderately complex queries run concurrently to present this information in the form of various reports on the web. (The app server is a separate machine and will connect to the DB through JDBC to create the HTML reports)

Any thoughts, ideas, comments would be appreciated.

Thank you,

Balazs Wellisch
Neu Solutions
balazs@neusolutions.com

  2. Re: Hardware performance

    Joe Conway <mail@joeconway.com> — 2003-07-17T04:52:13Z

    Balazs Wellisch wrote:
> first of all I'd like to thank everyone who responded to my earlier
> post. I have a much better understanding of postgres performance
> tuning now. In case anyone's interested we've decided to go with RH9
> and PostgreSQL 7.3 and we'll do the OS and DB tuning ourselves.
> (should be a good learning experience)

Good choice! I think you'll find that this list will be a great resource 
as you learn. One point here is that you should use 7.3.3 (latest 
release version) instead of the version of Postgres in the distribution. 
Also, you might want to rebuild the RPMs from source using
"--target i686".

> We have the budget for 5 drives. Does anyone have any real world
> experience with what hard drive configuration works best for
> postgres? This is going to be a dedicated DB server. There are going
> to be a large number of transactions being written to the database.

To an extent it depends on how big the drives are and how large you 
expect the database to get. For maximal performance you want RAID 1+0 
for data and WAL; and you want OS, data, and WAL each on their own 
drives. So with 5 drives one possible configuration is:

1 drive OS: OS on it's own drive makes it easy to upgrade, or restore 
the OS from CD if needed
2 drives, RAID 1+0: WAL
2 drives, RAID 1+0: data

But I've seem reports that with fast I/O subsystems, there was no 
measurable difference with WAL separated from data. And to be honest, 
I've never personally found it necessary to separate WAL from data. You 
may want to test with WAL on the same volume as the data to see if there 
is enough difference to warrant separating it or not given your load and 
your actual hardware. If not, use 1 OS drive and 4 RAID 1+0 drives as 
one volume.

You never want find any significant use of hard disk based swap space -- 
if you see that, you are probably misconfigured, and performance will be 
poor no matter how you've set up the drives.

> And there will be some moderately complex queries run concurrently to
> present this information in the form of various reports on the web.

Once you have some data on your test server, and you have complex 
queries to tune, there will be a few details you'll get asked every time 
if you don't provide them when posting a question to the list:

1) Have you been running VACUUM and ANALYZE (or VACUUM ANALYZE) at
    appropriate intervals?
2) What are the table definitions and indexes for all tables involved?
3) What is the output of EXPLAIN ANALYZE?

HTH,

Joe

  3. Re: Hardware performance

    Hannu Krosing <hannu@tm.ee> — 2003-07-17T07:56:49Z

    Joe Conway kirjutas N, 17.07.2003 kell 07:52:
> To an extent it depends on how big the drives are and how large you 
> expect the database to get. For maximal performance you want RAID 1+0 
> for data and WAL; and you want OS, data, and WAL each on their own 
> drives. So with 5 drives one possible configuration is:
> 
> 1 drive OS: OS on it's own drive makes it easy to upgrade, or restore 
> the OS from CD if needed
> 2 drives, RAID 1+0: WAL
> 2 drives, RAID 1+0: data

How do you do RAID 1+0 with just two drives ?

--------------
Hannu

  4. Re: Hardware performance

    Vincent van Leeuwen <pgsql.spam@vinz.nl> — 2003-07-17T10:14:16Z

    On 2003-07-16 19:57:22 -0700, Balazs Wellisch wrote:
> We're now stuck on the question of what type of RAID configuration to use
> for this server. RAID 5 offers the best fault tolerance but doesn't perform
> all that well. RAID 10 offers much better performance, but no hot swap. Or
> should we not use RAID at all. I know that ideally the log (WAL) files
> should reside on a separate disk from the rest of the DB. Should we use 4
> separate drives instead? One for the OS, one for data, one for WAL, one for
> swap? Or RAID 10 for everything plus 1 drive for WAL? Or RAID 5 for
> everything?
> 

We have recently run our own test (simulating our own database load) on a new
server which contained 7 15K rpm disks. Since we always want to have a
hot-spare drive (servers are located in a hard-to-reach datacenter) and we
always want redundancy, we tested two different configurations:
- 6 disk RAID 10 array, holding everything
- 4 disk RAID 5 array holding postgresql data and 2 disk RAID 1 array holding
  OS, swap and WAL logs

Our database is used for a very busy community website, so our load contains a
lot of inserts/updates for a website, but much more selects than there are
updates.

Our findings were that the 6 disk RAID 10 set was significantly faster than
the other setup.

So I'd recommend a 4-disk RAID 10 array. I'd use the 5th drive for a hot-spare
drive, but that's your own call. However, it would be best if you tested some
different setups under your own database load to see what works best for you.


Vincent van Leeuwen
Media Design - http://www.mediadesign.nl/

  5. Re: Hardware performance

    Joe Conway <mail@joeconway.com> — 2003-07-17T14:57:53Z

    Hannu Krosing wrote:
> How do you do RAID 1+0 with just two drives ?
> 

Hmm, good point -- I must have been tired last night ;-). With two 
drives you can do mirroring or striping, but not both.

Usually I've seen a pair of mirrored drives for the OS, and a RAID 1+0 
array for data. But that requires 6 drives, not 5. On non-database 
servers usually the data array is RAID 5, and you could get away with 5 
drives (as someone else pointed out).

As I said, I've never personally found it necessary to move WAL off to a 
different physical drive. What do you think is the best configuration 
given the constraint of 5 drives? 1 drive for OS, and 4 for RAID 1+0 for 
data-plus-WAL? I guess the ideal would be to find enough money for that 
6th drive, use the mirrored pair for both OS and WAL.

Joe

  6. Re: Hardware performance

    Adam Witney <awitney@sghms.ac.uk> — 2003-07-17T15:04:38Z

    > As I said, I've never personally found it necessary to move WAL off to a
> different physical drive. What do you think is the best configuration
> given the constraint of 5 drives? 1 drive for OS, and 4 for RAID 1+0 for
> data-plus-WAL? I guess the ideal would be to find enough money for that
> 6th drive, use the mirrored pair for both OS and WAL.

I think the issue from the original posters point of view is that the Dell
PE2650 can only hold a maximum of 5 internal drives


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  7. Re: Hardware performance

    Joe Conway <mail@joeconway.com> — 2003-07-17T15:09:44Z

    Adam Witney wrote:
> I think the issue from the original posters point of view is that the Dell
> PE2650 can only hold a maximum of 5 internal drives
> 

True enough, but maybe that's a reason to be looking at other 
alternatives. I think he said the hardware hasn't been bought yet.

Joe

  8. Re: Hardware performance

    Adam Witney <awitney@sghms.ac.uk> — 2003-07-17T15:20:42Z

    On 17/7/03 4:09 pm, "Joe Conway" <mail@joeconway.com> wrote:

> Adam Witney wrote:
>> I think the issue from the original posters point of view is that the Dell
>> PE2650 can only hold a maximum of 5 internal drives
>> 
> 
> True enough, but maybe that's a reason to be looking at other
> alternatives. I think he said the hardware hasn't been bought yet.

Actually I am going through the same questions myself at the moment.... I
would like to have a 2 disk RAID1 and a 4 disk RAID5, so need at least 6
disks....

Anybody have any suggestions or experience with other hardware manufacturers
for this size of setup? (2U rack, up to 6 disks, 2 processors, ~2GB RAM, if
possible)

Thanks

adam


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  9. Re: Hardware performance

    Jean-Luc Lachance <jllachan@nsd.ca> — 2003-07-17T16:13:27Z

    I am currious. How can you have RAID 1+0 with only 2 drives?
If you are thinking about partitioning the drives, wont this defeate the
purpose?

JLL

Joe Conway wrote:
> 
> [...]
> 2 drives, RAID 1+0: WAL
> 2 drives, RAID 1+0: data
> [...]

  10. Re: Hardware performance

    Joe Conway <mail@joeconway.com> — 2003-07-17T16:21:32Z

    Jean-Luc Lachance wrote:
> I am currious. How can you have RAID 1+0 with only 2 drives?
> If you are thinking about partitioning the drives, wont this defeate the
> purpose?

Yeah -- Hannu already pointed out that my mind was fuzzy when I made 
that statement :-(. See subsequent posts.

Joe

  11. Re: Hardware performance

    Joe Conway <mail@joeconway.com> — 2003-07-17T16:29:18Z

    Adam Witney wrote:
> Actually I am going through the same questions myself at the moment.... I
> would like to have a 2 disk RAID1 and a 4 disk RAID5, so need at least 6
> disks....
> 
> Anybody have any suggestions or experience with other hardware manufacturers
> for this size of setup? (2U rack, up to 6 disks, 2 processors, ~2GB RAM, if
> possible)

I tend to use either 1U or 4U servers, depending on the application. But 
I've had good experiences with IBM recently, and a quick look on their 
site shows the x345 with these specs:

•  2U, 2-way server delivers extreme performance and availability for 
demanding applications
•  Up to 2 Intel Xeon processors up to 3.06GHz with 533MHz front-side 
bus speed for outstanding performance
•  Features up to 8GB of DDR memory, 5 PCI (4 PCI-X) slots and up to 6 
hard disk drives for robust expansion
•  Hot-swap redundant cooling, power and hard disk drives for high 
availability
•  Integrated dual Ultra320 SCSI with RAID-1 for data protection

This may not wrap well, but here is the url:
http://www-132.ibm.com/webapp/wcs/stores/servlet/CategoryDisplay?catalogId=-840&storeId=1&categoryId=2559454&langId=-1&dualCurrId=73

Handles 6 drives; maybe that fits the bill?

Joe

  12. Re: Hardware performance

    Jean-Luc Lachance <jllachan@nsd.ca> — 2003-07-17T16:44:01Z

    Sorry for the redundant duplication of the repetition.
I should have read the follow-up messages.


Joe Conway wrote:
> 
> Jean-Luc Lachance wrote:
> > I am currious. How can you have RAID 1+0 with only 2 drives?
> > If you are thinking about partitioning the drives, wont this defeate the
> > purpose?
> 
> Yeah -- Hannu already pointed out that my mind was fuzzy when I made
> that statement :-(. See subsequent posts.
> 
> Joe

  13. Re: Hardware performance

    Jord Tanner <jord@indygecko.com> — 2003-07-17T16:54:26Z

    On Thu, 2003-07-17 at 08:20, Adam Witney wrote:


> Anybody have any suggestions or experience with other hardware manufacturers
> for this size of setup? (2U rack, up to 6 disks, 2 processors, ~2GB RAM, if
> possible)
> 
> Thanks
> 
> adam

Check out http://www.amaxit.com It is all white box stuff, but they have
some really cool gear.

-- 
Jord Tanner <jord@indygecko.com>

  14. Re: Hardware performance

    Andrew Sullivan <andrew@libertyrms.info> — 2003-07-17T18:41:52Z

    On Thu, Jul 17, 2003 at 07:57:53AM -0700, Joe Conway wrote:
> 
> As I said, I've never personally found it necessary to move WAL off to a 
> different physical drive. What do you think is the best configuration 

On our Solaris test boxes (where, alas, we do not have the luxury of
1/2 TB external RAID boxes :-( ), putting WAL on a disk of its own
yielded something like 30% improvement in throughput on high
transaciton volumes.  So it's definitely important in some cases.

A

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Liberty RMS                           Toronto, Ontario Canada
<andrew@libertyrms.info>                              M2P 2A8
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  15. Re: Hardware performance

    Robert Creager <robert_creager@logicalchaos.org> — 2003-07-18T03:23:08Z

    On Thu, 17 Jul 2003 16:20:42 +0100
Adam Witney <awitney@sghms.ac.uk> said something like:

> 
> Actually I am going through the same questions myself at the
> moment.... I would like to have a 2 disk RAID1 and a 4 disk RAID5, so
> need at least 6 disks....
> 
> Anybody have any suggestions or experience with other hardware
> manufacturers for this size of setup? (2U rack, up to 6 disks, 2
> processors, ~2GB RAM, if possible)
> 

We recently bought a couple of Compaq Proliant DL380 units.  They are
2u, and support 6 disks, 2 CPU's, 12Gb max.

We purchased 2 units of 1CPU, 4x72Gb RAID 0+1, 1Gb mem, redundant fans
and power supplies for around $11,000 total.  Unfortunately they are
running Win2K with SQLAnywhere (ClearQuest/Web server) ;-)  So far (5
months), they're real board...

Cheers,
Rob

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