[dba-Tech] Win2k Server and RAID

William Hindman wdhindman at bellsouth.net
Thu Feb 12 02:20:11 CST 2004


...hhhmmm ...lots and lots of "it depends" on some of these declarations
...try this source for pretty good overview of all the factors involved :
http://www.storagereview.com/guide2000/ref/hdd/perf/raid/index.html ...HTH
:)

William Hindman

----- Original Message ----- 
From: "Erwin Craps - IT Helps" <Erwin.Craps at ithelps.be>
To: "Discussion of Hardware and Software issues"
<dba-tech at databaseadvisors.com>
Sent: Thursday, February 12, 2004 2:52 AM
Subject: RE: [dba-Tech] Win2k Server and RAID


> RAID 5 is slower writing than a plain disk.
> It is advised not to use RAID 5 for databases files (SQL).
>
> The reasons for this is that RAID 5 does not only have to write but also
> calculate a parity bit each time you want to write. It's this
> calculation that slows down the writing to the disk.
> RAID 5 is also much slower when a disk of your set has crashed. For the
> same reason. When one of your disks has crashed it neads to calculate
> missing bit based on the parity bit each time you read.
> This is the general rule. There are however WRITE-CACHE available for
> hardware RAID controllers (as I have) but due to the fact this uses a
> buffer (128MB READ, 128MB write in my case) I'm supose, but not sure,
> some of that calculation delay if neutralized by the buffer. But again
> also in this case RAID 1 would be far superior in writing speed.
>
> So it is far better to put databases on to a mirrored disk set (RAID 1)
> if you want redundancy.
>
> The reason why SCSI is still far superior than ATA or SATA drive are
> mainly these.
> -No limit in the number of disks (as 4 in ATA or SATA)
> -Simultaneous access of ALL disks (2 for ATA, don't really know for SATA
> but I supose also 2)
>
>
> So if you build a mirror with ATA you must pay attention the two disk
> are on seperate controlers and are not in a master slave relation.
> Master slave means that the OS can only access one disk at the time. So
> if you create a mirror on two disks that are in master/slave your
> mirrored writes will be done sequential and not parralel.. This will
> dramaticaly slown down your writings.
> Same thing creating a RAID 5 of 3 or 4 ATA disk. The OS only access 2
> disks simulteneous, so you will get a drop in reading/writing.
>
> HOWEVER.
> There are companies that have RAID5 ATA/SATA controllers like adaptec.
> I supose that hardware RAID controllers using ATA or SATA have solved
> this issue.
> Note that a hardware RAID solution is always far superior than a
> software solution (altough I know 1 good advantage about software
> mirror). A hardware RAID solution spoofs the Os on a hardware level
> telling there is only one disk (example) and it should be considered
> that way.
> Meaning that the hardware controller probably solved the limitation in
> some way.
> But that I don't know.
> I'm one of those guys that will probably never use ATA or SATA for a
> server (unless a webserver with plenty memory).
>
> On the other hand, I'm buying piece by piece for my home music computer
> to have a RAID 5 with four 250GB SATA disk. I now have around 300GB of
> music and video files on my disks and I'm getting pretty scared because
> there no way I can backup this in a cheap way. AndI'm only half way
> putting my music collection on disk!!! So four 250GB SATA drives in a
> RAID 5 leaving me 750 GB would be nice....
>
> Erwin
>
>
>
>
>
>
>
>
>
>
> -----Original Message-----
> From: dba-tech-bounces at databaseadvisors.com
> [mailto:dba-tech-bounces at databaseadvisors.com] On Behalf Of Drew Wutka
> Sent: Thursday, February 12, 2004 3:07 AM
> To: Discussion of Hardware and Software issues
> Subject: RE: [dba-Tech] Win2k Server and RAID
>
> Not correct.  You can Mirror the OS 'volume' in Windows 2000 server,
> using the software RAID.  It just can't be part of a RAID 5 volume.
>
> Go into disk management, make the main drive, and your 'second' drive
> 'Dynamic Disks'.  It will require a reboot.  Once that is done, simply
> right click on your root partition, and tell it to Add Mirror.
>
> Piece of cake.
>
> As for your earlier question for performance issues, you won't really
> see any performance drop, but you will get performance gain on drive
> access.
> Mirrored will read twice as fast, striped will write twice as fast, and
> RAID
> 5 will read and write faster.
>
> Drew
>
> -----Original Message-----
> From: dba-tech-bounces at databaseadvisors.com
> [mailto:dba-tech-bounces at databaseadvisors.com]On Behalf Of John Bartow
> Sent: Wednesday, February 11, 2004 2:03 PM
> To: Discussion of Hardware and Software issues
> Subject: RE: [dba-Tech] Win2k Server and RAID
>
>
> William,
> My understanding is that when using software RAID 1 Windows OS can not
> be on a mirrored drive. When using hardware RAID 1 it can. is this
> correct?
>
> John
>
> > -----Original Message-----
> > From: dba-tech-bounces at databaseadvisors.com
> > [mailto:dba-tech-bounces at databaseadvisors.com]On Behalf Of William
> > Hindman
> > Sent: Wednesday, February 11, 2004 1:24 PM
> > To: Discussion of Hardware and Software issues
> > Subject: Re: [dba-Tech] Win2k Server and RAID
> >
> >
> >
> > ...it takes up cpu cycles ...but if your server is primarily a file
> > server rather than applications oriented, the added cycles won't be
> noticed.
> >
> > William Hindman
> > Government is not reason, government is not persuasion, government is
> > force. It is a dangerous servant." G. Washington
> >
> > ----- Original Message -----
> > From: "John Bartow" <john at winhaven.net>
> > To: "_DBA-Tech" <dba-tech at databaseadvisors.com>
> > Sent: Wednesday, February 11, 2004 12:25 PM
> > Subject: [dba-Tech] Win2k Server and RAID
> >
> >
> > > Does configuring RAID 1 with Win2k Server without a dedicated RAID
> > > card
> > have
> > > any major drawbacks?
> > >
> > > TIA
> > > John
> > >
> > >
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> > >
> >
> >
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>
>
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