RAID 4Si RAID controller & DS2100

[Lacrosse]

If I wanted a DS2100 with 2 channels using mirroring with the 4Si card would I need 2 4Si cards and then config DS2100 with split bus and the mirror images to each controller. Also can I then create a logical volume across several primary images striping the data across disks...please advise the best way to do this along with anything else that I might of missed

[Brian M Rawlings]

Assuming this is an HP-UX system, ONE 4Si card is ordinarily used to drive multiple DS2100s, rather than the other way around. With the four seperate SCSI channels coming off the card, you get higher availability if you RAID across multiple chassis.

For what you are describing, use standard UltraSCSI LVD cards, and use either mirrordisk/ux to do LVM mirroring across the two halves of the DS2100, or across two seperate DS2100s (for higher availability and no single point of failure). Or, on 11i, use the "light" version of Veritas Volume Manager that is included, to mirror across the two SCSI buses for free.

From your question, you seem to be approaching mirroring or RAID-5 protection from a different direction than the designers intended. What I have described is the way that most people would do RAID or mirroring, or at least much more in line with the intended use of each of these different cards.

Hope it helps. --bmr

[Brian M Rawlings · Accepted solution]

To directly answer your question, however, theoretically you shouldn't need two 4Si cards, you should be able to do "RAID 1/0" across any two drives in the DS2100, so you would use two of the four SCSI connections from the 4Si, one to each half of the DS2100.

I seem to recall that there are issues with dual-initiating with the DS2100, however, and I'm not sure that seperatly initiating each half from one card is supported. I don't know why it wouldn't be, but I don't really think you gain anything until you actually mirror to a drive in a different chassis.

If you're just looking for cheap mirrored storage, like I said, use standard UltraSCSI LVD cards and do OS mirroring (free, on 11i, if you use the VVM "lite" product).

--bmr

[Ron Lawson_1]

DS2100 does not support split bus configurations. Were you thinking of the DS2300?

In either case, RAID4Si cards can only have one connection to a given SCSI bus, because all channels of the card use SCSI ID 7. If you use a DS2300 (or an SC10) in split bus mode, you can connect two channels of the RAID 4Si to the JBOD, and mirror disks from one side to the other.

[Vincent Farrugia]

Hello,

The ds2100 is a JBOD, and has only 1 controller, so no split-bus/full-bus modes exist (if you want, it is always in full-bus mode).

The best way for HA is to connect the ds2100s on 2 separate channels on 1 4Si. You can also daisy-chain the ds2100 and connect them to 1 channel, treating 8 disks on 1 single channel instead of 4 disks per channel. But that is no good for HA.

HTH,
Vince

[Lacrosse]

So based off of what I have read can I have 4 seperate DS2100's 1 off each channel on the 4si and have the primary image on one DS2100 and the mirror image on the other DS2100. Then I can repeat on the other 2 channels???

[Vincent Fleming]

Yes. You've got it right.

[Ron Lawson_1]

One other thing to know -- with RAID 4Si there is a limit of 8 LUNs (logical drives) that can be seen by HP-UX -- with all 4 DS2100s loaded with disks, you will have 16 disks and 8 mirror pairs, so you will be at the max.

You could not expand this configuration to have 2 DS2100's on each channel and do the same RAID 1 configuration -- you'd have to look into using RAID 1+0 for something like that.

[Brian M Rawlings]

One last thing, the 4Si does not only do mirroring (raid 0/1), but it can do raid-5 as well. This would let you do four-drive raid-5 sets, one from each channel, as one LUN (and total useable space equal to 3 drives).

In this way, the 8 LUN limitation doesn't impact you as bad, and you could actually run two DS2100s on each channel before you ran out of LUNs. This is actually quite a bit of storage.

You need at least three drives to do raid-5 (ideally in three different DS2100s, so if you don't need all this space and all these LUNs, just go with mirrored (raid 0/1) across a pair of chassis on two channels.

One note of caution: this is your cheapest raid protection, but it has these drawbacks:
1> Single point(s) of failure (the 4Si raid controller itself)
2> Performance: if you put a lot of storage behind one overworked controller, and try to drive a lot of I/O, it will be slow.

For not too much money, you can see how this works for you, but if you end up needing no single point of failure HA, or lots more performance, you'll want a VA7410 array, or the current king in the small space (this week), the EMC CX600.