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 > > > > > > > > > _______________________________________________ > > > dba-Tech mailing list > > > dba-Tech at databaseadvisors.com > > > http://databaseadvisors.com/mailman/listinfo/dba-tech > > > Website: http://www.databaseadvisors.com > > > > > > > > > _______________________________________________ > > dba-Tech mailing list > > dba-Tech at databaseadvisors.com > > http://databaseadvisors.com/mailman/listinfo/dba-tech > > Website: http://www.databaseadvisors.com > > > > > > > _______________________________________________ > dba-Tech mailing list > dba-Tech at databaseadvisors.com > http://databaseadvisors.com/mailman/listinfo/dba-tech > Website: http://www.databaseadvisors.com > > > > _______________________________________________ > dba-Tech mailing list > dba-Tech at databaseadvisors.com > http://databaseadvisors.com/mailman/listinfo/dba-tech > Website: http://www.databaseadvisors.com > _______________________________________________ > dba-Tech mailing list > dba-Tech at databaseadvisors.com > http://databaseadvisors.com/mailman/listinfo/dba-tech > Website: http://www.databaseadvisors.com >