MD3000i and iSCSI Question

Also we are seeing the write cache suspened.

Read cache:                            Enabled                       
         Write cache:                           Enabled (currently suspended) 
            Write cache without batteries:      Disabled                      
            Write cache with mirroring:         Enabled (currently suspended) 
         Flush write cache after (in seconds):  10.00                         
         Dynamic cache read prefetch:           Enabled  

Dell says this is not user configurable.

Have you checked to see if there is a problem with your cache battery?

Just a quick note, you write "All of these are on one subnet for the iscsi", thats a big "no no". Each port on the controller on the MD3000i should be on a separate subnet, so you will need two subnets. each nic on the client should be on different subnets. Like this:

C(ontroller)1:P(ort)1 10.0.0.1
C1:P2 10.0.1.1
C2:P1 10.0.0.2
C2:P2 10.0.1.2

N(ic)1: 10.0.0.20
N(ic)2: 10.0.1.20

Then you make sure that both nics logs on to both controllers, you can verify that from the MD3000i managment application. Done right you will have the same write and read speeds, and as an added bonus you will have complete loadbalancing, fail over and no single point of failure.

/Adam

Also we are seeing the write cache suspened.   Read cache:                            Enabled                                 Write cache:                           Enabled (currently suspended)              Write cache without batteries:      Disabled                                   Write cache with mirroring:         Enabled (currently suspended)           Flush write cache after (in seconds):  10.00                                   Dynamic cache read prefetch:           Enabled     Dell says this is not user configurable.

Those entries for the write cache saying "currently suspended" doesn't look right. Did support have any feedback on why it says that? It looks to me like it has suspended (effectively disabled) write cache, which could play a role in your very low write performance.

Cache settings, including write cache (enabled | disabled) are end user configurable. See the Set Virtual Disk command in the CLI guide:

http://support.dell.com/support/edocs/systems/md3000i/en/CLI/PDF/CLIMR2g.pdf

Write cache will be suspended if there is a battery error or if the battery is currently in a learn cycle (the latter only applies to the Gen 2 update which introduced Smart Battery support).

Is the storage array in a Needs Attention state?

Dave

I am experiencing exactly the same problem. Here goes an excerpt from the profile data:

         Battery status:              Optimal                      
         Location:                    RAID Controller Module 0     
         Age:                         27 days                      
         Days until replacement:      Not applicable               
         Last learn cycle:            14 January 2009              
         Next learn cycle:            15 April 2009                
         Weeks between learn cycles:  13                           
         Part number:                 PN JY200                     
         Serial number:               SN 047118334386              
         Vendor:                      VN DELL                      
         Date of manufacture:         01 March 2008                


         Battery status:              Battery learning             
         Location:                    RAID Controller Module 1     
         Age:                         27 days                      
         Days until replacement:      Not applicable               
         Last learn cycle:            14 January 2009              
         Next learn cycle:            15 April 2009                
         Weeks between learn cycles:  13                           
         Part number:                 PN JY200                     
         Serial number:               SN 0471182J4767              
         Vendor:                      VN DELL                      
         Date of manufacture:         01 February 2008             

      Virtual Disk name:                      test-RAID1-100GB                                
         Virtual Disk status:                 Optimal                                         
         Read cache:                            Enabled                       
         Write cache:                           Enabled (currently suspended) 
            Write cache without batteries:      Disabled                      
            Write cache with mirroring:         Enabled (currently suspended) 
         Flush write cache after (in seconds):  10.00                         
         Dynamic cache read prefetch:           Enabled

I guess there must be a problem with one of the batteries (although everything is marked as "optimal"): if the last learn cycle took place on January 14 and the next one is scheduled for April 15, why is it still in "learning" state?

Cheers,

     Gonçal

I had some oddites with this when I did the second gen fw updates.

Only thing support and I ever figured out was to leave the san up for a long time after the update to complete the learn cycles.

Shutting it off before the learn cycle completes seems to lead to the oddites.  best of luck, keep us informed please on how this progresses.

I do think your slow write issue is being caused be this as well.

Just a reminder that when you fail a controller you are supposed to do a  "redistribute controller ownership / prefered path" on all the VD's handled by the MD3000i..... 

It may have fixed it, but you may be forcing all I/O to the controller that was left online is all.

Thanks for the reminder! Indeed, I had forgotten to do it in the first instance, but luckily I noticed and corrected the mistake when I double-checked the configuration :)

Hi!

I have actually removed the offending controller and inserted it back in. This has solved the issue (!) and now writing speeds are back to decent levels (e.g. ~50MB/s on a 3-disk RAID5 volume on ext3 filesystem).

In the mean time, we have also opened a ticket with technical support, just to see if they can find out whether there is anything wrong with the hardware.

Cheers!

Well, the MD3000i SAN is designed to never be shut off.

Might be obvious but I just wanted to point that out. ;-)

Not so obvious....    I do keep our redundant offline MD3000i turned on now though, since I had issues with the controller battery.   :)  In testing and experience,  those learn cycles are not to be interrupted or missed, and can cause issues.