RAID 1 question, about hot swapping

[DeadSeaSquirrels]

I have a question about RAID 1. If I setup a RAID 1 array with 2 harddrives, does that mean both harddrives will have the same exact data simultaenously, or are there times when the second hard drive hasn't fully copied everything on the first harddrive yet. For example: I setup the array, I move a gigantic file into my C: Drive, when I am moving the files to the C: drive lets say, does the RAID controller automatically copy everything also on the mirror drive...or does the RAID controller use some sort of intelligence to do some copying now, and then some copying later.

My second question is about hot swapping then, which relates to the first one. How do you make a RAID array hot swappable. Is that just a feature of the RAID card, so you'd need to get a RAID card that does hot swapping. Because if hotswapping is to work, I would imagine then that the second (or third, or however many harddrives you have), won't ALWAYS have all the information as the "main" harddrive, since you might pull it out at any time, or put it in at any time. Can somebody explain to me how hot swapping works, and if my a RAID controller will always copy everything immediately, or do some intelligent tasks management. Thanks for the information everyone.

 

[SCSIRAID]

Both drives in a RAID 1 array contain exactly the same data. You havent said whether you are asking about a simple ATA SW RAID colution or an intelligent RAID controller with Cache. I will assume the simple SW RAID.

A single write from the OS to the RAID driver results in two writes being issued - one to each of the drives. There is a small window of time when the two write commands are outstanding that the two drives can have different data. The driver will not indicate command complete to the os until the writes to both drives are complete.

As to hot swap.... the array isnt hot swappable.... a drive is hot swappable. If you pull an active drive then the array will go critical i.e. non redundant. Plugging the drive back in will start a rebuild where the data on the remaining drive will be copied to the new drive and redundancy will be restored.

 

[DeadSeaSquirrels]

So if I pulled a hot swappable drive from an array, and replaced it with a totally fresh, newly formatted drive, it would take the RAID Controller card, or the OS quite a bit of time to get everything setup on the new drive, is that correct?

Also what makes a drive hot swappable or not...is it just the physical design of the connection?

 

[ozone13]

You are also not specifying if this is ata, scsi, or sata raid 1 hot swapping. ATA hotswapping is not possible, some of the new sata supports hot swapping, but it depends on the models.....and scsi you should be able to hot swapping.

 

[Blain]

What about replacing a dead drive in an ATA RAID 1 configuration... not "hot-swapped"?

Does the data from the good drive get transfered over to the new drive automatically upon rebooting?

 

[ndee]

Originally posted by: Blain
What about replacing a dead drive in an ATA RAID 1 configuration... not "hot-swapped"?

Does the data from the good drive get transfered over to the new drive automatically upon rebooting?

With the Fasttrack TX2000 controller, you have to shut down the computer, change the defect harddisk and then when you boot, you can "rebuild" your harddrive.

 

[DeadSeaSquirrels]

Thanks Blain for asking that question...I was curious about that too. So I guess after you have a dead drive and you install a new fixed drive, it will take some time while the new drive gets mirrored.

As for not specifying which drives I meant, ATA, SATA, SCSI...well that's because I don't know anything about hot swapping, so I couldn't ask the "right question." But now I know.

 

[Blain]

If you don't have drives configured in a RAID array, and are running Windows 98, you could use something like this removable tray to toss data onto an extra drive. I guess it would work with other OS without being "hot swappable".

 

[ozone13]

Originally posted by: Blain
If you don't have drives configured in a RAID array, and are running Windows 98, you could use something like this removable tray to toss data onto an extra drive. I guess it would work with other OS without being "hot swappable".

No, it probably wouldn't work. Yes, you can use it to pull out the drives easier, but you would not be able to use it on ata raid drives. Its a limitation of the ata spec. What that site is probably referring to is "hotswapping" within win98 just as a regular drive, not part of a raid configuration.