dekroon
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How do RAID controllers work?
In one server, I have an integrated (into the Tyan S2469UGN motherboard) Adaptec 2010S Ultra 320 SCSI controller with two RAID 1 arrays.
In another server, I have an integrated (into the SuperMicro X6DHR-TG motherboard) Adaptec 2025SA SATA controller also with two RAID 1 arrays.
Here's what I'd like to know:
How does the RAID controller keep track of which drive is the source and which the spare? (e.g., Does it write some kind of signature on the drive? In the case of the SCSI card, does it look at its SCSI address?)
I’ll probably have more questions as I figure out exactly what I need to know, but that ought to get us started.
Thanks in advance.
Joe
In another server, I have an integrated (into the SuperMicro X6DHR-TG motherboard) Adaptec 2025SA SATA controller also with two RAID 1 arrays.
Here's what I'd like to know:
How does the RAID controller keep track of which drive is the source and which the spare? (e.g., Does it write some kind of signature on the drive? In the case of the SCSI card, does it look at its SCSI address?)
I’ll probably have more questions as I figure out exactly what I need to know, but that ought to get us started.
Thanks in advance.
Joe
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Okay - anybody have any experience to the contrary? Or can you assist in verifying what leew suggests?
Thanks.
Thanks.
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ASKER
Thanks, all.
Assuming RAID 1 here... (i.e. two disks (or partitions) mirrored)
If you use a RAID *controller* card, there's no "master" and "slave". A Raid 1 mirror means every single byte is written to both drives the same - and can be read back from either. If a drive fails, replace it, and the mirror will be rebuilt.
If you use *software* RAID it's a bit more complex coz you don't normally mirror the entire drive, rather, you make partitions on the drive, then mirror these. Within this situation, however, any two mirrored partitions are, again, just the same as each other. You should, however, read up on how any given operating system copes with mirroring of *boot* partitions. Some need you to take extra steps to ensure that in the event of one drive failing, you can boot off the other.
If you establish a s/w mirror within Windows, this is important.
I just made a mirrored installation of a RedHat linux system, and it's much more like the "controller" situation. You do the mirroring at the "FDISK" stage (Druid) of the installation, *before* you create the root, boot, and other partitoins you need/want. You create two "raidable" partitions (one on each disk) then you create the mirror pair linking the two, and then you define this new "raid-ed" partition as "boot", "/" etc.
(In the case of a raid controller card, the operating system sees the combined RAID array as a single disk).
If you use a RAID *controller* card, there's no "master" and "slave". A Raid 1 mirror means every single byte is written to both drives the same - and can be read back from either. If a drive fails, replace it, and the mirror will be rebuilt.
If you use *software* RAID it's a bit more complex coz you don't normally mirror the entire drive, rather, you make partitions on the drive, then mirror these. Within this situation, however, any two mirrored partitions are, again, just the same as each other. You should, however, read up on how any given operating system copes with mirroring of *boot* partitions. Some need you to take extra steps to ensure that in the event of one drive failing, you can boot off the other.
If you establish a s/w mirror within Windows, this is important.
I just made a mirrored installation of a RedHat linux system, and it's much more like the "controller" situation. You do the mirroring at the "FDISK" stage (Druid) of the installation, *before* you create the root, boot, and other partitoins you need/want. You create two "raidable" partitions (one on each disk) then you create the mirror pair linking the two, and then you define this new "raid-ed" partition as "boot", "/" etc.
(In the case of a raid controller card, the operating system sees the combined RAID array as a single disk).
ASKER
Thanks for the comments, ccomley.
I'm using the RAID controller and not the OS to create and manage my array. Once the array is created, the OS sees it as one drive.
When you first create a RAID 1 array, one drive is designated as source and the other as spare.
I'm using the RAID controller and not the OS to create and manage my array. Once the array is created, the OS sees it as one drive.
When you first create a RAID 1 array, one drive is designated as source and the other as spare.
Well, you can try a test.
Take the system down. Pull one of the drives. Will it still boot on the other?
Try it again, the other way around. Will it still boot?
If it'll boot and run of either of the disks, it's truly symmetrical and you don't care if it prefers to think of one as primary andone as slave.
If it won't boot and run off either, you probably need to find this out *now* not when one of them fails.
The other thought that occurs to me is, if it is thinking "Main" and "Slave", does it run off a single disk until/unless it fails then switch, or does it run in trad style all the time, i.e. writes are sent to both disks, reads are *shared* between them. Coz that gives you the speed boost. :-) But if you're not in it for performance (and if you were, maybe you'd be Raid-5ing?) then you probably don't care.
Take the system down. Pull one of the drives. Will it still boot on the other?
Try it again, the other way around. Will it still boot?
If it'll boot and run of either of the disks, it's truly symmetrical and you don't care if it prefers to think of one as primary andone as slave.
If it won't boot and run off either, you probably need to find this out *now* not when one of them fails.
The other thought that occurs to me is, if it is thinking "Main" and "Slave", does it run off a single disk until/unless it fails then switch, or does it run in trad style all the time, i.e. writes are sent to both disks, reads are *shared* between them. Coz that gives you the speed boost. :-) But if you're not in it for performance (and if you were, maybe you'd be Raid-5ing?) then you probably don't care.
ASKER
https://www.experts-exchange.com/questions/21339042/Can-I-pull-a-RAID-drive-as-a-backup-image.html