Does PostgreSQL Stores its database in multiple disks?

Discussion:

(too old to reply)

Igor Maciel Macaubas

2004-10-01 21:01:23 UTC

Hi Guys,

I have a PostgreSQL server, running 7.4.2, that will store a really large amount of data (200GB) being migrated from an Oracle database. I have a machine with two 120GB Ultra ATA IDE disks, and I'd like to know if PostgreSQL could split it over both disks (that gives me 240GB or storage). Does he do this automatically ?
Or I'll have to split it manually, creating symbolic links on my file system (ext3)?
Does anyone ever stored a database (see, it's ONE database only, not a cluster) on multiple disks ?

What about PgSQL 8? It'll include this feature?

Thanks!

Regards,
Igor
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Björn Lundin

2004-10-01 21:09:13 UTC

Permalink

Have you considered Raid? Raid 0 or 1 (I keep forgetting which)
will make the 2 disks to appear as one (The other will mirror one disk)

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Heather Johnson

2004-10-01 21:17:44 UTC

Permalink

Could you configure the two volumes as one volume with RAID? If so, then
Postgres shouldn't require any special adjusting to accomplish what you
are after.

Heather Johnson
Senior Database Programmer
New York Post

Post by Igor Maciel Macaubas
Hi Guys,
I have a PostgreSQL server, running 7.4.2, that will store a really
large amount of data (200GB) being migrated from an Oracle database. I
have a machine with two 120GB Ultra ATA IDE disks, and I'd like to know
if PostgreSQL could split it over both disks (that gives me 240GB or
storage). Does he do this automatically ?
Or I'll have to split it manually, creating symbolic links on my file system (ext3)?
Does anyone ever stored a database (see, it's ONE database only, not a
cluster) on multiple disks ?
What about PgSQL 8? It'll include this feature?
Thanks!
Regards,
Igor
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Igor Maciel Macaubas

2004-10-01 21:28:57 UTC

Permalink

Hi,

Heather, I might be able to do it. Let me check .. I can buy a cheap RAID
IDE controller and try to mount everything as one.

I was looking at the change log of postgresql 8, and figured out that it
supports tablespace now, giving me the flexibility of storing my tables in
different disks and even different directories if I want.

So, I'm thinking in, instead of migrating it from oracle to 7.4.2, migrate
it directly to 8.0 and be a beta tester for 8.0. that would be a great
experiment, don't you think?
Is anyone here using pgsql 8.0 in production now? I'm already using it in my
development environment, around 80 tables but just a few megabytes of data
(it's development). Is anyone here using it in a real world application by
now?

Regards,
Igor
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----- Original Message -----
From: "Heather Johnson" <***@nypost.com>
To: "Igor Maciel Macaubas" <***@providerst.com.br>
Cc: <pgsql-***@postgresql.org>
Sent: Friday, October 01, 2004 6:17 PM
Subject: Re: [ADMIN] Does PostgreSQL Stores its database in multiple disks?

Post by Heather Johnson
Could you configure the two volumes as one volume with RAID? If so, then
Postgres shouldn't require any special adjusting to accomplish what you
are after.
Heather Johnson
Senior Database Programmer
New York Post

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Christopher Browne

2004-10-01 22:10:12 UTC

Permalink

Post by Igor Maciel Macaubas
Heather, I might be able to do it. Let me check .. I can buy a cheap
RAID IDE controller and try to mount everything as one.

You'd be about as well off, if you're running Linux, to use the "md"
RAID driver that simulates RAID in software.

Post by Igor Maciel Macaubas
I was looking at the change log of postgresql 8, and figured out that
it supports tablespace now, giving me the flexibility of storing my
tables in different disks and even different directories if I want.
So, I'm thinking in, instead of migrating it from oracle to 7.4.2,
migrate it directly to 8.0 and be a beta tester for 8.0. that would be
a great experiment, don't you think?
Is anyone here using pgsql 8.0 in production now? I'm already using it
in my development environment, around 80 tables but just a few
megabytes of data (it's development). Is anyone here using it in a
real world application by now?

Nobody should be considering using 8.0 for anything called "production
use" at this point in time, because it is NOT guaranteed that there
will be an upgrade path to the "official" release.

Now, I'm possibly 'somewhat conservative,' as someone that wouldn't
want to call a system 'production' if it's using cheapo IDE drives.

But what you're proposing isn't merely a matter of 'trying to jump the
learning curve;' you're tempting, instead, the "learning cliff," and
the results of problems, there, are that instead of scuffing your
knees, you wind up falling 8 stories and going "splat."

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Christian Fowler

2004-10-01 23:56:31 UTC

Permalink

Igor,

I would recommend you investigate LVM:

http://www.tldp.org/HOWTO/LVM-HOWTO/

This enables you to string multiple physical units into a single volume -
as well as expand and grow the volume. I am unsure about postgres
consequences of this for as much data as you have, so I will leave it up
to others to comment about this.

However, my recommendation is for a modest investment of a third 120GB
drive and a RAID card, you could do RAID 5 with 3 disks and get 240GB of
storage.

Post by Igor Maciel Macaubas
Hi Guys,
I have a PostgreSQL server, running 7.4.2, that will store a really
large amount of data (200GB) being migrated from an Oracle database. I
have a machine with two 120GB Ultra ATA IDE disks, and I'd like to know
if PostgreSQL could split it over both disks (that gives me 240GB or
storage). Does he do this automatically ? Or I'll have to split it
manually, creating symbolic links on my file system (ext3)? Does anyone
ever stored a database (see, it's ONE database only, not a cluster) on
multiple disks ?
What about PgSQL 8? It'll include this feature?
Thanks!
Regards,
Igor
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Stephen Frost

2004-10-02 00:20:53 UTC

Permalink

Post by Igor Maciel Macaubas
I have a PostgreSQL server, running 7.4.2, that will store a really large amount of data (200GB) being migrated from an Oracle database. I have a machine with two 120GB Ultra ATA IDE disks, and I'd like to know if PostgreSQL could split it over both disks (that gives me 240GB or storage). Does he do this automatically ?
Or I'll have to split it manually, creating symbolic links on my file system (ext3)?
Does anyone ever stored a database (see, it's ONE database only, not a cluster) on multiple disks ?
What about PgSQL 8? It'll include this feature?

An alternative might be to use some kind of LVM (such as device
mapper/LVM2 under Linux) to combine the two disks into one logical
device.

Stephen

Scott Marlowe

2004-10-02 00:40:02 UTC

Permalink

I'd normally advise against ATA drives in a production system. If you
must use them, make sure the write cache is turned off or you risk data
corruption should the machine lose power.

Post by Igor Maciel Macaubas
and I'd like to know if PostgreSQL could split it over both disks
(that gives me 240GB or storage). Does he do this automatically ?

Not automatically, no. With 8.0's table space feature, you could put
half your database tables etc... on one drive and one half on another.
This would require you to keep track of how much your putting in one or
other, and could get rather tedious.

If you don't mind shutting down the database and copying / linking the
individual table files you could do that, but again, that's gonna
require you to do a lot of housekeeping on your own.

Lastly, you could use some kind of RAID or LVM setup to accomplish this.

For testing purposes running this on a RAID-0 with linux's MD or LVM
modules should work fine. But RAID-0 has no redundancy and a single
drive failure means the whole set goes down.

With 4 drives you could set up a RAID 1+0 array (or 0+1) and place your
data there. That setup could survive a single drive failure and keep on
going.

If your database will be writing a lot, it would be well worth your
while to investigate a SCSI RAID controller with battery backed cache
set to write back.

Post by Igor Maciel Macaubas
Or I'll have to split it manually, creating symbolic links on my file system (ext3)?

That would be a lot of work.

Post by Igor Maciel Macaubas
Does anyone ever stored a database (see, it's ONE database only, not a
cluster) on multiple disks ?

Standard answer is use RAID arrays.

Post by Igor Maciel Macaubas
What about PgSQL 8? It'll include this feature?

Not really. While it will support table spaces, the job of combining
multiple drives into one large logical drive is the domain of your
operating system / underlying hardware.

I recommend the LSI MegaRAID series controllers, and a few other folks
on the list have had good luck with the Escalade IDE RAID controllers,
which aren't the toys most IDE RAID controllers are, they support
multiple RAID levels as well as battery backed cache.

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