multiple tablespaces containers on SAN

Thread view:

Enable EMail Alerts

Start New Thread

Thread rating:

paul - 27 Oct 2006 09:45 GMT

Hi,
i want to know if this is better to split a tablespace into several
containers while the database are on san disk.
And how can i configure optimally the values for prefetch and extend ?

thx

Reply to this Message

Lew - 27 Oct 2006 16:26 GMT

I would say the answer is almost always yes. How you set it up exactly
depends on the way your logical disk volumes and file systems are
mapped to the backend storage packs. The values for prefetch and
extentsize are somewhat (but not entirely) related to how the data will
be accessed.

Lew

> Hi,
> i want to know if this is better to split a tablespace into several
> containers while the database are on san disk.
> And how can i configure optimally the values for prefetch and extend ?
>
> thx

Reply to this Message

Ian - 27 Oct 2006 18:52 GMT

> Hi,
> i want to know if this is better to split a tablespace into several
> containers while the database are on san disk.

Assuming you have DB2_PARALLEL_IO set properly (to enable DB2 to issue
multiple I/O requests to each container) then the answer is no.
Spreading your tablespace across multiple containers in the same
file system will result in I/O contention at the disk level.

Use 1 container per RAID array in the SAN device (note, multiple LUNs
may exist on a single RAID array, so make sure you understand the
mapping from file system -> LUN -> RAID array).

> And how can i configure optimally the values for prefetch and extend ?

Extent size should be set to the strip size (or a multiple thereof) of
the RAID arrays in your SAN device. Prefetch should be set to ensure
that all disks are serving data for a prefetch request.

Reply to this Message

paul - 30 Oct 2006 10:58 GMT

hi
thanks for your comment, i'll check this with the san administrator

paul

> > Hi,
> > i want to know if this is better to split a tablespace into several
[quoted text clipped - 14 lines]
> the RAID arrays in your SAN device. Prefetch should be set to ensure
> that all disks are serving data for a prefetch request.

Reply to this Message

mike - 31 Oct 2006 08:36 GMT

> Use 1 container per RAID array in the SAN device (note, multiple LUNs
> may exist on a single RAID array, so make sure you understand the
> mapping from file system -> LUN -> RAID array).

The DB2 publications continue to advise to use one container per
tablespace when using RAID devices.

Is that always the best advice ?

Reply to this Message

Mark A - 31 Oct 2006 20:28 GMT

>> Use 1 container per RAID array in the SAN device (note, multiple LUNs
>> may exist on a single RAID array, so make sure you understand the
[quoted text clipped - 4 lines]
>
> Is that always the best advice ?

Probably is the correct advise for most systems, depending on the throughout
of you RAID controller.

However, unless you have a data warehouse and are doing a lot of table
scans, it doesn't matter much, one way or the other. Check your buffer pool
hit ratio, and if it is above 95%, don't even worry about it.

Reply to this Message