Thread: Can postgresql store its data on raw device now?

Hello,

    I have an problem: can postgresql store its data on the raw disks now?

    I have checked the mail list and manual, but haven’t found the
answer. In some early mails, they mentioned pg didn’t support this
character. But how about now? Raw disk may reduce the risks brought by
file system, so I want to use it to store my data.

    Thanks a lot.

Yours Sincerely,
Liz

On Tue, Jun 9, 2009 at 8:49 AM, Gurjeet Singh<singh.gurjeet@gmail.com> wrote:
> It still doesn't support raw device.

Nor is it ever likely to. Filesystems are vastly superior now than
when certain other DBMSs were designed to use raw devices, and for
PostgreSQL to replace the average filesystem now with something as
reliable, performant and well tested would take a significant amount
of effort for little, if any, gain.

--
Dave Page
EnterpriseDB UK:   http://www.enterprisedb.com

On Tue, Jun 9, 2009 at 4:14 AM, Dave Page<dpage@pgadmin.org> wrote:
> On Tue, Jun 9, 2009 at 8:49 AM, Gurjeet Singh<singh.gurjeet@gmail.com> wrote:
>> It still doesn't support raw device.
>
> Nor is it ever likely to. Filesystems are vastly superior now than
> when certain other DBMSs were designed to use raw devices, and for
> PostgreSQL to replace the average filesystem now with something as
> reliable, performant and well tested would take a significant amount
> of effort for little, if any, gain.

As the 'solid state drive' train continues to leave the station, this
will become more and more true.  Flash based SSD and hard drives have
very different operating characteristics that require cooperation
between the device, filesystem, and o/s if you want things to work
optimally.

Why reinvent the wheel?  I think the trend is in in the other
direction...applications are trying to dispatch as much work in
dealing with I/O into the kernel and out of user space as possible.

merlin

lizzymy@gmail.com (Lizzy M) writes:
>     I have an problem: can postgresql store its data on the raw disks now?
>
>     I have checked the mail list and manual, but haven�t found the
> answer. In some early mails, they mentioned pg didn�t support this
> character. But how about now? Raw disk may reduce the risks brought by
> file system, so I want to use it to store my data.

No, this has not changed, and if anything, it is *less* likely to
change than ever.

Twenty years ago, filesystems were sufficiently fragile, unreliable
and slow that DBMS vendors found it worthwhile to avoid the risks by,
in effect, implementing their own filesystems as part of the DBMS.

- Since then, OS vendors have found it to be in their interests to
  improve both the robustness and performance of their filesystems,
  which has substantially diminished the would-be benefits.

- Compound this with the factor that implementing your own filesystem
  adds substantially to the complexity of managing and deploying the
  DBMS.

The two really interesting filesystems these days are ZFS and OCFS:
  http://en.wikipedia.org/wiki/ZFS
  http://en.wikipedia.org/wiki/OCFS

It seems much more useful to allow the OS vendors to improve their
filesystems, which helps us, than to use raw partitions, which
requires:

 a) Creating a portable framework for OS-agnostic access to raw
    partitions

    (because Linux != FreeBSD != Solaris != Windows NT != AIX != ...)

 b) Implementing our own filesystem atop raw partitions

 c) Implementing our own filesystem management tools (e.g. - like cp,
    rm, ..., since our OS tools won't work)

As an aggregate, this would add an extraordinary amount of work, and
with the improvements that have taken place lately, it is not evident
that this would buy us *any* of:
 a) Improved performance
 b) Improved reliability

Indeed, I think we could reasonably expect for there to be a
significant period of time during which performance and reliability
would be *degraded* by such an effort.
--
let name="cbbrowne" and tld="linuxdatabases.info" in name ^ "@" ^ tld;;
http://cbbrowne.com/info/rdbms.html
"I'm guilty of a lot of things, but I didn't ever do that.''
-- Bill Clinton, on why he had astroturf lining the back of his pickup
   truck
[In fact, he _DID_ do this, thus making life creepier than fiction...]