Re: Minimal configuration, suggestions wanted.

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From: ben brugman (ben_at_niethier.nl)
Date: 04/08/04 

Date: Thu, 8 Apr 2004 11:16:47 +0200

>
> RAID 1 OS / SQL Binaries
> RAID 1 SQL Transaction Logs
> RAID 10 DATA, TempDB
>

What about :
> > 4 Backupdata
> > 5 Transactionlog backup

I still have difficulty in understanding why different groups
offer more 'protection' than less different groups.

In your schema at least 8 disks are needed to realise
the solution. (1 each for the RAID 1 solution and at least
four for the RAID 10 solution. This is often the maximum
number of disks a 'simple' RAID box supports).

IF (this is supposed by me, so you can point out the
error or mistake in my reasoning.)
IF I put everything OS/Log/Data on a single group of
RAID disks the worst that can happen is that two mirrored
disks fail, resulting in the dataloss since the last backup and
move to outside the system.
But with the proposed system of having OS/Log/Data each on
their own group, the risk of losing the Log is the same because
losing the mirrored disk (with only the logs) gives us the
same amount of dataloss as with everything on the same group.
I very strongly feel that I AM MISSING SOME UNDERSTANDING
of this situation.
(Offcourse if the volumes of data and log become larger and
performance is an issue, I would go with more groups and understand
the reasons for this.).

My question is : Why is it wrong to put OS/Log/Data on a single
group of disks ?
(What is the risc of this ? Or why are there more riscs for this
than 3 groups of disks ?)

Everybody (books, discussions, usegroups) that this should
not be done, but except for performance the reason(s) is (are) not
explained.

Thanks again for your time,
and sorry to go on on this subject, but I really would like to
understand it.
ben brugman

> --
> Andrew J. Kelly SQL MVP
>
>
> "ben brugman" <ben@niethier.nl> wrote in message
> news:c50moh$gtq$1@reader11.wxs.nl...
> > Going with your suggestions,
> > suppose you have split the total RAID device in 3 groups
> > of disks (fysical separate), how would you place
> >
> > 1 OS
> > 2 Logging
> > 3 Data
> > 4 Backupdata
> > 5 Transactionlog backup
> >
> > Have I missed anything ?
> > Or are 2 groups enough ?
> > Or do I need more groups ?
> >
> >
> > > on how much data you are willing to loose. If you can afford to loose
> up
> > to
> > > 15 minutes worth of transactions then use a 15 minute interval etc.
Just
> >
> > If I go from estimates of MTBF of disks the chance of
> > losing a mirrored disk is extremely small. So the chance
> > of loosing up to 15 minutes of data is extremely small.
> > Loosing the complete system because of a major
> > dissaster (fire for example) looks more likely and then
> > you loose everything since the last time you brought
> > the backup to outside of the 'box' or the computerroom.
> > Because for a minimal system bringing the data out of the
> > room more than once or twice a day would probably be a
> > problem.
> >
> > (Calculation for 2 disks failing, assuming a MTBF of 300000 hours,
> > that a failed disk is spotted with in 24 hours. I get a failure of
> > two disks every once in 1/(24/300000)^2 days = 156250000 days)
> >
> > Two of my problems :
> >
> > 1. Backup of the transaction log is not a 'backup' but a 'move' of the
> > 'content',
> > so how do I protect the backup of the transaction log, because at that
> > moment
> > it is the only 'copy' of that data in existence. (Still mirrored I would
> > suggest).
> >
> > 2. If part of the chain of transactionlogs (active of backupped) is lost
> the
> > datafiles are worthless, so I do not understand that the datafiles
> > should be on a separate disk.
> > (Performance not being a consideration).
> >
> > Thanks for your thoughts.
> >
> > ben brugman
> >
> >
> >
> >
> >
> >
> > "Andrew J. Kelly" <sqlmvpnoooospam@shadhawk.com> wrote in message
> > news:uRptBADHEHA.2260@TK2MSFTNGP09.phx.gbl...
> > > Keep in mind that a server with a 200GB db and moderate load may not
be
> > the
> > > same for a 10GB db with light load and this is addressing the latter
as
> > you
> > > asked. A RAID 0+1 will give the most fault tolerate Raid with good
> > > performance as well. If the load is light enough (not a lot of
> > > transactions) then you can probably get away with a good size (meaning
#
> > of
> > > disks not size of disks) RAID 0+1 or even 1+0 that has everything on
it.
> > > But it is usually best to place the logs on their own RAID 1 and
> separate
> > > from the data for performance reasons. With a minimal configuration a
> > good
> > > raid is essential along with proper backups. A full backup once a
night
> > is
> > > usually OK for most applications. The frequency of the log backups
> depend
> > > on how much data you are willing to loose. If you can afford to loose
> up
> > to
> > > 15 minutes worth of transactions then use a 15 minute interval etc.
Just
> > > ensure the backups are not done to the same drive the logs or data
> reside
> > > on.
> > >
> > > --
> > > Andrew J. Kelly SQL MVP
> > >
> > >
> > > "ben brugman" <ben@niethier.nl> wrote in message
> > > news:u1zBcW7GEHA.688@tk2msftngp13.phx.gbl...
> > > > Minimal configuration.
> > > > (Performance is not an issue).
> > > >
> > > > Dataloss should not happen. (But we do not account
> > > > for real dissasters, for example a big fire destroying
> > > > the complete production center, resulting
> > > > in the dataloss of 24 hours would be acceptable.)
> > > >
> > > > The shop runs 7 x 24 hours.
> > > > Most is done during office hours.
> > > > Some is done during all day.
> > > > At night the system must be available but it is
> > > > used very limited.
> > > >
> > > > Once a day a tape goes from the production machine to an
> > > > offsite safe.
> > > > The total amount of data has a disk footprint off
> > > > between 1 and 10 Gigabytes.
> > > >
> > > > Offcourse there is a production machine and
> > > > a standby machine probably in another location.
> > > > (The second machine will be used for testing and
> > > > practicing procedures.)
> > > >
> > > > Raid is required, raid protects agains single disks failures,
> > > > but what are the options for more protection ?
> > > > What configuration is considered minimal in these circumstances ?
> > > > Esspecially what to do with the disks ?
> > > > (OS / Logging / Data / Backupdata / Transactionlog backup) ?
> > > > What can be combined and what can not be combined ?
> > > > And how often to do the transactionlog backup ?
> > > > (Side question what "route" should the transactionlog(-backup)
> > > > take).
> > > >
> > > >
> > > > Keep in mind : We are looking for a minimal configuration.
> > > >
> > > > Later on we will also looking for a 'larger' configuration with
> > > > more performance, a larger database etc. (But still no super
> > > > configuration. Something like 100-200 Gigabyte and more load).
> > > >
> > > > Thanks for your thoughts,
> > > > ben brugman.
> > > >
> > > >
> > >
> > >
> >
> >
>
>

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