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Old 11-17-2008, 11:50 PM
KenShelby
 
Default Journal config for SAN array

The thread in this forum about using SSD for journals...

http://www.nabble.com/journal-on-an-ssd-to19411589.html

leads me to ask:

What is the best way to configure journals for about half a dozen servers
accessing some twenty file systems hosted on a RAID-5 SAN array? The array
holds relational databases which are used in an OLTP style by web-based
apps, so it sees lots of small-ish, nonsequential transactions. Presume the
array has enough physical disks and cache to provide normally acceptable
performance. None of the file systems on the array are shared: each file
system is mounted (and zoned and masked) to one and only one server, though
there may be several file systems on a server.

Thanks in advance!


-----
"You people from New Jersey are the Gypsies of the Galaxy!"

--
View this message in context: http://www.nabble.com/Journal-config-for-SAN-array-tp20525748p20525748.html
Sent from the Ext3 - User mailing list archive at Nabble.com.

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Old 11-22-2008, 10:23 PM
"Jordi Prats"
 
Default Journal config for SAN array

Hi,
There's not a single answer for this. It depends on each
configuration, for each SAN, for each SAN topology...

Is not that easy as it appears

regards,

--
Jordi http://systemadmin.es

On Tue, Nov 18, 2008 at 1:50 AM, KenShelby <kshelby@optonline.net> wrote:
>
> The thread in this forum about using SSD for journals...
>
> http://www.nabble.com/journal-on-an-ssd-to19411589.html
>
> leads me to ask:
>
> What is the best way to configure journals for about half a dozen servers
> accessing some twenty file systems hosted on a RAID-5 SAN array? The array
> holds relational databases which are used in an OLTP style by web-based
> apps, so it sees lots of small-ish, nonsequential transactions. Presume the
> array has enough physical disks and cache to provide normally acceptable
> performance. None of the file systems on the array are shared: each file
> system is mounted (and zoned and masked) to one and only one server, though
> there may be several file systems on a server.
>
> Thanks in advance!
>
>
> -----
> "You people from New Jersey are the Gypsies of the Galaxy!"
>
> --
> View this message in context: http://www.nabble.com/Journal-config-for-SAN-array-tp20525748p20525748.html
> Sent from the Ext3 - User mailing list archive at Nabble.com.
>
> _______________________________________________
> Ext3-users mailing list
> Ext3-users@redhat.com
> https://www.redhat.com/mailman/listinfo/ext3-users
>

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Old 11-23-2008, 02:06 PM
KenShelby
 
Default Journal config for SAN array

I'm not looking for a single "magic bullet" answer. Are there any guidelines
at all, any best practices that have been found over time to be a good place
to start? What I seek is either informed opinion or information - if it
exists - about how to make choices on EXT3 journal configuration for a SAN
installation.

- Ken


Hi,
There's not a single answer for this. It depends on each
configuration, for each SAN, for each SAN topology...

Is not that easy as it appears

regards,

--
Jordi http://systemadmin.es

On Tue, Nov 18, 2008 at 1:50 AM, KenShelby <kshelby@optonline.net> wrote:
>
> What is the best way to configure journals...


-----
"You people from New Jersey are the Gypsies of the Galaxy!"

--
View this message in context: http://www.nabble.com/Journal-config-for-SAN-array-tp20525748p20647102.html
Sent from the Ext3 - User mailing list archive at Nabble.com.

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Old 11-23-2008, 03:34 PM
Jure Pečar
 
Default Journal config for SAN array

On Sun, 23 Nov 2008 07:06:28 -0800 (PST)
KenShelby <kshelby@optonline.net> wrote:

>
> I'm not looking for a single "magic bullet" answer. Are there any
> guidelines at all, any best practices that have been found over time to
> be a good place to start? What I seek is either informed opinion or
> information - if it exists - about how to make choices on EXT3 journal
> configuration for a SAN installation.

Common sense and knowlege of your application are a good start.

You said that you have lots of random io, so I would be more concerned over
latency than bandwith. If your SAN provides you with good enough latency
then I wouldn't bother much about journal configs and go with defaults, but
if your SAN sits on something like iSCSI with noticeable latency then I'd
test a setup with journal on local disk, possibly even in full data
journaling mode. If I had the money I'd look into SSDs for that purpose,
either in form of SSD sata/sas drive or in form of PCIe card (fusion-io for
example).

--

Jure Pečar
http://jure.pecar.org/

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Old 11-24-2008, 02:22 AM
Andreas Dilger
 
Default Journal config for SAN array

On Nov 23, 2008 17:34 +0100, Jure Pečar wrote:
> On Sun, 23 Nov 2008 07:06:28 -0800 (PST)
> KenShelby <kshelby@optonline.net> wrote:
> > I'm not looking for a single "magic bullet" answer. Are there any
> > guidelines at all, any best practices that have been found over time to
> > be a good place to start? What I seek is either informed opinion or
> > information - if it exists - about how to make choices on EXT3 journal
> > configuration for a SAN installation.
>
> Common sense and knowlege of your application are a good start.
>
> You said that you have lots of random io, so I would be more concerned over
> latency than bandwith. If your SAN provides you with good enough latency
> then I wouldn't bother much about journal configs and go with defaults, but
> if your SAN sits on something like iSCSI with noticeable latency then I'd
> test a setup with journal on local disk, possibly even in full data
> journaling mode. If I had the money I'd look into SSDs for that purpose,
> either in form of SSD sata/sas drive or in form of PCIe card (fusion-io for
> example).

One important consideration is if you have hardware RAID-5/6, then it is
a bad idea to put the journal on the same device as the filesystem. That
causes a lot of read-modify-write of RAID stripes, and bad performance.
Much better to put the journal on a RAID-1 device.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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