Tag Archives: iSCSI

Migrating NetApp cloned LUNs for iSCSI boot

If you are booting a Linux system via iSCSI (using Broadcomm or Intel iSCSI-bootable Ethernet), certain information specific to your system is embedded in the Linux configuration during the OS installation. If you then clone that LUN and try to boot it with another system, all hell breaks loose. The system starts to boot and then “learns” during the boot process it’s old IP and MAC and iSCSI IQN information, which essentially makes it switch boot luns mid way through! Imagine the disaster that makes when you boot from LUN X and it starts to modify LUN Y!

Here are my quick notes on what it takes to “break” the relationships embedded on the boot/root LUN.

  • Install CentOS to HostA, booting from iSCSI NetApp LUN “lunA”
  • Create a lun clone “lunB”, and then do a non-space-efficient lun clone split in order to get rid of the snapshot dependencies between the systems.
  • Boot the HostA from the clone/copy “lunB”
  • Edit /boot/grub/grub.conf for new IP, new Ethernet MAC, new IQN. MAC addresses must be lowercase!
  • Edit /etc/iscsi/initiatorname.iscsi
  • Edit /etc/sysconfig/network-scripts/ifconfig-eth*  with the updated ethernet macs, IPs
  • Edit /ets/sysconfig/network for new hostname
  • Shutdown -h
  • boot the second host (HostB) from the modified copy (LunB) to test.

This is for a non-GUI system. If you are running a GUI and the second host doesn’t have the same video card, that will break and you will have to reconfigure X.

 

Installing Windows 2008 R2 to an iSCSI target (Broadcomm NetExtreme II)

We have a lab at work for the various sales engineers to use. We’ve done a home-brew boot-from-iSCSI farm of servers so we can change boot luns pretty easily, based on a NetApp FAS270 (old cheap but reliable for the moment.)

I had the iSCSI initiator in the BIOS set up and could see it logging into the FAS270. The problem was that if I had the CDROM selected as secondary boot (so I could install an operating system to the new LUN), it would attempt to boot from iSCSI (good!), fail (normal, no OS yet), and then log out of the iSCSI connection before continuing to boot from the CDROM (secondary device). Windows wouldn’t see the target device for installation.

If I put the CDROM first, then the NetExtreme BIOS wouldn’t log into the iSCSI target, so Windows installation again would not see the target device for installation. This differs from IBM x3650 M2/M3 servers which will initialize the iSCSI connection first, no matter what order the boot device is, and work “as expected”.

The trick is to put the CDROM second, but hit “CTRL-D” after the initial login to the iSCSI initiator. The iSCSI boot ROM actually warns you “Hit Ctrl-D if you don’t want to boot from the iSCSI target” or similar. Hitting Ctrl-D tells the Broadcomm chipset to skip iSCSI boot, but stay logged in to the target. So the target LUN is visible, the system boots from CDROM, and the Windows installation can install to the iSCSI device.

 

DroboElite Review Part 3: Functionality and Performance meet Ease of Use

This is a long overdue post.

Back in October I took advantage of DataRobotic’s evaluation program, obtaining a DroboElite for a 30-day period for testing.

I finished up my testing and data gathering in November.  My plans included comparing the iSCSI performance of the iSCSI DroboElite with server-based iSCSI target solutions such as Nexenta.

Life, work (my day job) and the sometimes unavoidable complexities of building  a home server pushed my final writeup out. And out… more family and more work.

Here it is, mid February, and Data Robotics has made new announcements of business-class offerings, and I started to feel pretty bad about blowing off my final words on the DroboElite. I know a few people over at Drobo, and they went out of their way to make sure that I could get access to the DroboElite, and I didn’t live up to my end of the deal in the time frame that I suggested.

I took extensive performance data, driven by the benchmark “fio” written by Jens Axboe. It’s a very flexible benchmarking tool, I suggest you check it out.  I will not present the data here, however, as there were serious outliers in every dataset that I took, that I later attributed to the compiled version of “fio” I was running on my test platform (Mac mini).

I tested with 5 new Samsung Spinpoint F3 HD103SJ 1TB drives, trying both single and dual parity modes.

Single host performance was excellent, with both random and sequential read and write performance being very good, both for larger block sizes (bandwidth) and smaller block (IOPs). I was able to get a very high percentage of the maximum expected bandwidth from the larger block testing, anywhere from 60-90MB/s. Mixed read-write performance was significantly less optimal, specifically 4k and 8k mixed random read-write.

Multiple host performance mirrored  the results of the single-host performance. With 2 hosts doing large-block sequential IO, I was able to get nearly 100MB/sec combined between the two hosts. Mixed read-write performance was less than optimal, similar to the single host testing.

The above performance patterns, while not sufficient for “enterprise” levels of IO from several hosts, is certainly viable for SMB and professional offices.  More importantly, like it’s smaller SOHO brethren, the DroboElite is easy to set up, and a Drobo customer isn’t going to need a consultant to get it going, and to maintain it.

Conversion to double parity, in my case going from 4+1 RAID 5 up to 4+2 double parity RAID,  was painless. A couple of clicks in the GUI, and off you go. Conversion back to single parity was just as easy. Compare this to ZFS, where you cannot convert a RAID-Z directly, nor can you expand it. You can replace drives (increasing in size along the way) or add other RAID-Z groups to a zpool, but you cannot made the RAID-Z group “wider” or add additional parity.

Speaking of ZFS, I struggled for weeks (several 10′s of hours all in all) coming up with a ZFS solution that I was happy with. If I were a business professional, those hours would have been lost to the business.  I’m still not completely satisfied with my ZFS file server. If I owned this Drobo, I would have spent my time playing with other things, rather than rebuilding file servers over and over in order to come up with a satisfactory ZFS solution for my needs.

Where does the DroboElite fit today given the new announcements? Looking at the specs, it seems that the DroboElite is either morphing into, or being replaced by the B800i. I have my suspicions as to what the actual details are, but will withhold speculation until I learn more.

Disclosure: I’ve worked with a couple of people who are now at Data Robotics. They made it possible for me to do this evaluation. But they haven’t asked me to color my responses in any way.

Product Reviews Coming Soon: Hybrid Laptop Drive, DroboElite

It’s my birthday and I’m playing with toys!

Seagate Momentus XT Hybrid Drive

First, I just bought a Seagate Momentus XT 500GB Solid State Hybrid Drive. This drive adds 4GB of NAND Flash to act as an intelligent read cache to existing high density 500GB 7200 spindle-based technology.

I am very excited to be dropping this into my MacBook Pro, so I’ll need to pull together some basic benchmarks on my existing Western Digital Black 7200rpm drive so I can compare the “before vs. after”.

Data Robotics DroboElite iSCSI disk array

I’ve also taken the opportunity to evaluate the DroboElite.  If you haven’t heard, Data Robotics is running an evaluation program, where you can get your hands on the DroboElite for 30 days. Check it out here. This array supports multi-host iSCSI access, which makes it a potential player in offices where one may have more than one server. It’s also VMware certified… a big plus!

I’ve got about 4 weeks to take it for a spin in my environment, with a mix of hosts. It’s going to be tight, but I’ll post here as I check out its ease of use, performance and real world “care and feeding” overhead.