SUMMARY: Photons vs. EMC on Sun

From: Damon LaCaille (
Date: Mon Jun 14 1999 - 22:22:16 CDT

Several weeks ago I posted a question regarding the use of both the new Sun A5100 Photon disk array (fiber channel) and an EMC symmetrix disk array on the same box in the hopes that the 5100 (or multiple 5100s) could some day replace the EMC box.

We have an Ultra-Enterprise 4000 with 3.5GB of memory, 8 processors @250MHz, an EMC w/ 288 GB (mirrored capacity of 144), and now a Sun A5100 Photon disk array w/ 250GB (mirrored capacity of 125GB). The machine is currently running Solaris 2.5.1 HW11/97, soon to be upgraded to 2.6.

The EMC is connected via 4 SCSI controllers, and the Photon is connected via redundant fiber channel controllers, each fiber channel controller is also on a separate IO card in the 4000 for additional redundancy. Each channel sees all drives, so Veritas volume manager (which comes with the 5100s by the way) automatically configures it for alternate pathing (or some term similar).

The main focus of the question was if we could put additional memory onto the 4000 to compensate for the loss of the EMC cache (512MB) on the EMC box itself if we were to get rid of it.

We had our Informix DBA bump up the allocation value of Informix to 1.5 GB, so as soon as the system comes up, 1.5GB is pretty much unusable by anything but the database. We experienced very poor response times from the A5100s when I originally configured them. After doing some investigation (I'm new to Veritas by the way), we discovered that if you want to access the Veritas volume manager disks through raw partitions, you need to use the /dev/vx/rdsk links instead of the /dev/vx/dsk links. Apparently Veritas creates both for you and you decide how you want to access them. After we changed the links and made sure the internal memory was being utilized fully, we ran some tests.

The results (drum roll please): The EMC and the Sun A5100 Photon came in almost identical in speed in almost every way. Long sequential read/writes, short bursts of random I/O, reading/writing to same disks, and reading/writing to opposite disks (EMC to Photon and vice versa). The EMC seemed to be less than 5% faster on the writes, but the Photon was at least 10-20% faster on most reads. The EMC partitions were striped against 4 disks, each on a separate controller. The Photon partitions were striped against 7 disks, which is optimal for the 5100's configuration. All disks were mirrored on their respective boxes as well.

So if I had to choose, I'd go completely with A5100s at this point. The tricky part now is to get the OS off of the EMC and onto a second A5100. The database is a fairly simple job with a backup and restore to the new partitions. And on top of this, Sun completely supports the A5100s, it's less expensive on a yearly contract basis to support the 5100 than the EMC, it has a higher throughput for the amount of money we can spend, and comes with great software that allows easy partitioning and alternate pathing. EMC charges big bucks to offer you the alternate pathing solution. Don't forget that the 4000's and 5100's can fit in the new Sun 72" rack as well (drool)...

I must also say that our EMC box is currently running on 4 20MByte/sec SCSI channels, while the A5100 can theoretically push 200MByte/sec if the drives could spin fast enough. Since both fiber channels see both sides of the 5100, the manual says that you can set it up to go 200MByte/sec. (Somebody correct me if I'm wrong)

As a final comment. I'm not bashing EMC. I know EMC has fiber channel as well and can probably match the 5100 in almost everything if not beat it. EMC's are good boxes if you can afford them, and they're great if your #1 priority is to get the fastest possible speed and you're willing to pay the outrageous premium. However, I believe the law of diminishing returns hits you pretty hard in this area, especially when comparing the Photon to the EMC. For the amount of money we were willing to pay, the EMC box couldn't come close to the benefits and cost of the Photon.

Can you really tell that you're going faster if you're doing 180mph versus 170mph? Would you trade that extra 10mph for added comfort (Sun support), easy handling (Veritas) and better looks (matches your Enterprise system colors), and a much smaller price tag?

Any additional comments/corrections would be appreciated to the above information if anything is incorrect.


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