Performance is another reason I DON"T mirror the DB, if all I've got to
work with is RAID-5.
RAID-5 is relatively slow for WRITE activity, DEPENDING on your hardware
implementation of RAID. A lot of people don't realize that. When you
are writing to a RAID-5 disk, it requires writing to multiple physical
drives and writing the parity info before the job is finished. It takes
longer than writing to a raw disk or writing to a RAID-1 (physically
mirrored) drive.
If it's internal hard drives on a Winders box, and performance is an
issue, I take a couple of drives OUT of the RAID-5 configuration, and
have TSM do the mirroring on two raw drives. It's noticeably faster.
On your average, low priced DELL or COMPAQ type Windows server, most
people use RAID controller cards for internal disks that cost about
$300. They cost only $300 FOR A REASON: they don't provide cache (or
enough of it) to overcome the WRITE penalty on the RAID-5.
If your RAID is in a properly-striped FaSTT or EMC or Shark box, that's
an entirely different story. They have enough cache memory in the
controllers (with battery backup) to overcome a lot of the WRITE
overhead for RAID. That's why they cost more.
Pretty much, if you are installing TSM new, on a relatively small
configuration (say less than 50GB in the TSM DB), on relatively new
hardware, it will just work. Nobody is around in the middle of the
night to watch it, and it just doesn't matter if your backups or
expiration runs longer by 15 minutes.
It's when you get large TSM DB's, and you notice that EXPIRATION runs
way too long, or your DB backups start taking too long, or you have
literally hundreds of clients, then you start worrying about ways to
speed things up. What is "too long", well.......that depends on you.
If it isn't causing a problem, and you're getting everything completed
every day, it's not "too long".
Wanda Prather
"I/O, I/O, It's all about I/O" -(me)
-----Original Message-----
From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf Of
Paul Fielding
Sent: Friday, April 08, 2005 2:54 PM
To: ADSM-L AT VM.MARIST DOT EDU
Subject: Re: Question on SETUP
I'd be interested to know if anyone has done real performance testing
re:
using TSM mirroring with a RAIDed backend.
People on the list are raising valid reasons for using TSM mirroring on
top
of RAIDed disk (though I think that it's important for people to
understand
exactly *why* they are doing this and ensure that they've laid out the
disk
they're using appropriately - eg. mirroring to a bunch of files in the
same
FS is probably a bad idea).
The next question though, would be what sort of performance hit might
one
take in doing this? Obviously not a simple question as there are
factors
such as whether or not the disk being mirrored is same type, is the
mirrored
data going out the same scsi/fc wire, etc. That being said, if those
factors are considered and mostly mitigated, do people find anything
else in
this scenario that might cause a performance hit, or do things seem to
fly
along quite nicely?
regards,
Paul
----- Original Message -----
From: "Prather, Wanda" <Wanda.Prather AT JHUAPL DOT EDU>
To: <ADSM-L AT VM.MARIST DOT EDU>
Sent: Friday, April 08, 2005 12:21 PM
Subject: Re: [ADSM-L] Question on SETUP
> Yet another opinion:
>
> If you are running TSM HSM, that requires 24x7 availability. Then you
> should mirror both DB and logs.
>
> If you are NOT running TSM HSM, a lot of TSM installations can
actually
> afford to have TSM down a couple of hours.
> SO what I usually do, when I have the DB on a RAID device, is just to
> mirror the recovery log.
>
> That way, if you DO lose the DB due to some type of logical
corruption,
> you can always restore from your last DB backup, and roll forward from
> the log. So you lose no data, just some time.
>
> It's adequate protection, if you can afford the time.
>
> (That assumes you run in ROLLFORWARD mode, which you SHOULD be doing,
> and you are very religious about your DB backups, which you SHOULD
be!)
>
>
>
>
>
>
> -----Original Message-----
> From: ADSM: Dist Stor Manager [mailto:ADSM-L AT VM.MARIST DOT EDU] On Behalf
Of
> Joerg Pohlmann
> Sent: Thursday, April 07, 2005 10:38 PM
> To: ADSM-L AT VM.MARIST DOT EDU
> Subject: Re: Question on SETUP
>
>
> Hi Paul. From bitter experience I have been saved by TSM mirroring on
> nicely protected disks. I have had complete filesystems clobbered as
> result of other hardware failures, nothing to do with the disks - have
> had
> filesystems damaged on AIX and also Windows. TSM mirroring is such a
> superb, inexpensive protection against these other failures that I
> always
> recommend TSM mirroring. It's also quite inexpensive give todays cost
of
> disk storage, including Shark. And yes, on a Shark I would create four
> filesystems (/tsmdb1 /tsmdb2 /tsmlog1 /tsmlog2 - Windows an D: E: F:
and
> G: drive) so that the 1s and 2s (or the E: and G: drive) are in
> different
> LSSs.
>
> And yes, I wear belt and suspenders.
>
> Joerg Pohlmann
> 604-535-0452
>
>
>
>
> Paul Fielding <paul AT FIELDING DOT CA>
> Sent by: "ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU>
> 2005-04-06 23:25
> Please respond to
> "ADSM: Dist Stor Manager"
>
>
> To
> ADSM-L AT VM.MARIST DOT EDU
> cc
>
> Subject
> Re: Question on SETUP
>
>
>
>
>
>
> I don't see the value in mirroring the db and logs if they're placed
on
> Shark disk. The purpose of TSM's mirroring is to provide disk
> redundancy
> in case of disk failure. However, the Shark provides it for you.
Why
> add
> the extra overhead of software mirroring when the hardware does a
> valiant
> job in the background. The Quck Start recommendation doesn't take into
> account that your disk is already protected...
>
> regards,
>
> Paul
>
> ----- Original Message -----
> From: "Jones, Eric J" <eric.j.jones AT LMCO DOT COM>
> To: <ADSM-L AT VM.MARIST DOT EDU>
> Sent: Wednesday, April 06, 2005 2:56 PM
> Subject: [ADSM-L] Question on SETUP
>
>
>> Good Afternoon.
>> I was asked to setup a new TSM server 5.2.2 on a AIX 5.2 server.
>> My question has to do with setting up the DB, LOG and DISKPOOL.
>> On our current servers which run the same O/S and TSM version the DB,
> LOG
>> and DISKPOOL are mirrored.
>> On the new system I'm setting up these are all going to reside on a
> IBM
>> SAN(SHARK) which is all RAID.
>> Is there any reason to mirror them since the mirror would be on the
> same
>> set of drives(space was already allocated on a LUN)?
>> I understand it's always good to mirror(protect DB, LOG, DISKPOOL)
but
> in
>> this case I'd have to mirror to the same set of disk since I was only
>> allocated a set of space to work. In the TSM class it also
> recommended
>> that you mirror for protection.
>> I'm in the middle of reading the "Quick Start" for the second time
and
> I
>> see they recommend "Mirror your Database and recovery log for "Server
> and
>> storage pool protection". I wanted to make sure there was not a
>> performance issue or anything else.
>>
>> Have a Great Day,
>> Eric Jones
>>> * eric.j.jones AT lmco DOT com
>>> *: 607-751-4133
>> Cell : 607-972-7621
>>
>
|
