Using a journaled fs versus raw logical devices

Using a journaled fs versus raw logical devices

Post by Wouter Vissch » Sat, 11 May 1996 04:00:00



Who has opinions or experience  with the following:

Older unices had insecure file systems so Sybase decided to bypass the OS
and directly access the disk through the raw device driver. The mapping
of the device driver to disk used te be fairly direct.

More modern Unices have logical volumes with raw logical devices , an sometimes
other features like disk mirroring ( on the OS level ).
Writing to a raw logical device  does not bypass the OS but has to go through
the logical volume manager, diskmirroring manager ( layer ).
If you use a  file on a file system all you add is 1 extra layer.

Wat are the advantages, disadvantages if a journaled file system (veritas) is
used instead of a raw logical device.

Sybase still recommends raw logical device instead of a filesystem.

I have to decide what to use on HPUX 10.01 files on an VXFS files system or
raw logical volumes.

In the past I used always to start with raw devices but ended using a mix
of raw devices and and file just to get the space needed.

Wouter

#include <stddisclaimer.h>       This might not be the view of my employer.

 
 
 

Using a journaled fs versus raw logical devices

Post by Pablo Sanch » Tue, 14 May 1996 04:00:00



> Who has opinions or experience  with the following:

> Older unices had insecure file systems so Sybase decided to bypass the OS
> and directly access the disk through the raw device driver. The mapping
> of the device driver to disk used te be fairly direct.

> More modern Unices have logical volumes with raw logical devices ,
> an sometimes other features like disk mirroring ( on the OS level
> ).  Writing to a raw logical device does not bypass the OS but has
> to go through the logical volume manager, diskmirroring manager (
> layer ).  If you use a file on a file system all you add is 1 extra
> layer.

> Wat are the advantages, disadvantages if a journaled file system (veritas) is
> used instead of a raw logical device.

> Sybase still recommends raw logical device instead of a filesystem.

> I have to decide what to use on HPUX 10.01 files on an VXFS files system or
> raw logical volumes.

> In the past I used always to start with raw devices but ended using a mix
> of raw devices and and file just to get the space needed.

On IRIX, XFS is journaled.  Recognize that that feature makes the
journaling part synchronous.  It ought to be safe to use a journaled
system but do test your system throughput though.

Pablo Sanchez              | Ph # (415) 933.3812        Fax # (415) 933.2821

===============================================================================
I am accountable for my actions.   http://reality.sgi.com/pablo [ /Sybase_FAQ ]

 
 
 

Using a journaled fs versus raw logical devices

Post by r l re » Tue, 14 May 1996 04:00:00



Quote:>Who has opinions or experience  with the following:
>Older unices had insecure file systems so Sybase decided to bypass the OS
>and directly access the disk through the raw device driver.

Nothing whatsoever to do with security.  Speed and safety, since
Sybase was controlling the file i/o, and not trusting the operating
system to do the physical writes to disk when essential.  And
yeah, you drop one level of redirection.

Sybase does NOT recommend using the file system for the same
reasons it always has.  In the event of a crash, you run a much
higher risk of losing data.                    

There is no good reason whatsoever for using the file system for
production databases.  I have heard of success in Solaris using the
operating system mirroring instead of Sybase mirroring, but
even so - mirror the raw device, and avoid use of the file system.

Quote:>In the past I used always to start with raw devices but ended using a mix
>of raw devices and and file just to get the space needed.

A gentle suggestion that your site needs to plan better; and be willing to
pay for more disk (for more raw device) when neccessary instead
of scronging for pieces of file systems.  It makes no sense to
run a high-end (high$$$) DBMS if you're going to go cheap for
a few meg or gig of disk - especially at today's disk prices.

--

copyright 1996 by r l reid
                    microtonal resources and what not at:
       http://www.panix.com/~ro/  -OR-  http://woof.music.columbia.edu/~rlr/

 
 
 

1. Raw versus fs : Pure provocation or real knowledge ?

While I was reading an article on :

http://www.ixora.com.au/tips/creation/raw_datafiles.htm

I found :

<cut>
All operating systems maintain a read/write lock for each file system
based datafile. Read/write locks allow multiple concurrent readers, but
ensure exclusive access for each writer. This means that concurrent
readers and writers must contend for file access.
</cut>

It is first time I hear than Unix is doing exclusive flock() to update
an Oracle file. The article is so interesting, and the author is so
obviously commited to RAW devices, than it is worth clarifying this
point.

Does anybody has enough knowlegde (and guts) to assert or not this point
?

B. Polarski

http://www.geocities.com/bpolarsk

Sent via Deja.com http://www.deja.com/
Before you buy.

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