The professional blog of Christopher Randel

ZFS RAID-Z partitioning efficiency

I’ve finally got around to setting up FreeNAS at home, and testing it out.

Overall so far, I’m very impressed. Tons of features. Where I’ve been a bit hung up is the mystical, magical ZFS.

I’ve been exploring just how it works, and I’ll try to explain it in simpler terms, and fail miserably.

Using ZFS, you create Virtual devices [Vdev] that are some sort of storage.

It could be a chunk of a hard drive, a whole hard drive, or even a hardware or software LUN, which is some volume recognized by the BIOS or RAID card configuration.

Further, for example, If I had 8 hard drives, I could use the first 10GB of each drive to make a RAID-Z2 (which is comparable to RAID6, 2 parity devices], which would give me 80GB total space, and 60GB usable, with 20 GB lost to parity.

Once you have your Virtual devices set up, you can combine them into a “Pools”. Pools are made up of one or more Vdevices. What those devices are [Single Disk, RAID-Z, RAID-Z2, etc] doesn’t matter.

So with the infinite number of configurations I can make, whats the most disk space I can get, while say, using RAID-Z2. That is, I can handle two drive failures without any data loss.

On my test rig at home, I have 9 disks as follows: 640GB, 500GB, 500GB, 500GB, 250GB, 250GB, 250GB, 120GB, 120GB.

To brain this, I ended up putting it down on an excel spreadsheet, with a different color for each drive.

And played around with the different things I could do.

Even while wasting 140GB on the biggest drive, none of them could beat

I’ve been throwing this one around a few days, but couldn’t quite wrap around it in my head. But after some nerding around, the answer rings true.

The most efficient way to use your different sized hard drives  for ZFS is to use as many disks as possible in each virtual device.

Using nginx to add SSL

I’m not going to lie, like every other network guy, I googled my way through this one.

nginx is one of my favorite new applications. I’ve been using it in a limited fashion to do proxying for websites from the internet DMZ to internal, secured network without poking more holes in the firewall architecture.

Let me note that I understand nginx is designed to do much more than just proxying, and apache can probably do the same thing, but the simplicity and transparency it has with apache configs is pretty priceless. I know a few rails/ROR people love it for the the same reason; it’s incredibly simple and easy to pick up if you’re familiar with apache.

I shamelessly followed the slicehost walkthrough on adding SSL in front of your site via proxying found here. I also followed their steps for adding the SSL cert here.

Take a peek at my finished config.

root@proxy:/etc/nginx/sites-available$ cat site.domain.com

server
{
	listen 80;
	server_name site.domain.com;

	location / {
		rewrite ^/(.*)$ https://site.domain.com/$1 redirect;
		   }

}

server
{
	listen 443;
	server_name site.domain.com;

	ssl on;
	ssl_certificate /etc/nginx/ssl/certs/site.crt;
	ssl_certificate_key /etc/nginx/ssl/private/site.key;
	keepalive_timeout 210;
	add_header Front-End-Https on;

	location / {
	proxy_pass http://yourinternernalapp.domain.com:10000;
	proxy_redirect on;
	proxy_set_header Host $host;
	}
}

It’s something I expected for me to claw through, but I finished it in about 5 minutes.  I think this is awesome, since you can have the SSL in front of your site in the backend, and not have to worry about changing 10 different certificates in your cluster, just the two+ at your load balancer(s).

Dell Support Round Three

This is pretty genuinely terrifying. Enterprise class stuff that doesn’t seem to be well tested. Running 10K SAS Seagate Drives … and this guy sends me a disk that updates the firmware to just about every enterprise class disk out there.

System – You are now being connected to an agent. Thank you for using Dell Chat

Derrick – Hello, thank you for contacting Dell’s Enterprise Chat Support. My name is Chris. Once the chat session is completed, a transcript will be sent to chris.randel. Please give me 2 to 3 minutes to access your system details and contact information.

Chris – Hi Derrick. I’ve got another failed hard drive from this system I need to rma.

Derrick – How can I help you today? Please provide as much information as possible, such as error messages, symptoms, and any troubleshooting steps that may have been taken up to this point.

Chris – One of the hard disks was failed and trying to reinitialize over and over. I’ve replaced it with a spare.

Derrick – Can you confirm the address that this needs to go to?

Derrick – [Address]

Chris  - something like that.

Derrick – One moment while i get this setup..

Derrick – Since this is your 2nd problem within a few weeks i would make sure you have all the drivers/firmware update for the system.

Derrick – Especially the firmware specifically for the hard drives.

Chris – do you have a link i can go about checking that?

Derrick – http://ftp.us.dell.com/SATA/DELL_MULTI-DEVICE_A09_R211868.EXE

Chris – hmm. its a FreeBSD box

Derrick – That fine, this creates a bootable CD for the hard drive firmware.

Derrick – neat. i’ll try that out

Derrick – I just figured the whole batch of disks is going slowly. We have two of these PE2950s that are identicle, and they both have been throwing about one disk a week for the last two weeks.

Chris – Using both for developing environments in VM.

Derrick – Yea, that could be part of the reason is the firmware..

Derrick – There has been numerous occasions with some of the SAS and SATA drives that had problem with the amber light and basically reseating the drive would fix it only for a short time but the firmware is what helped it be more stable.

Chris – Seems strange the firmware would fail after they have been up for the last two years? I’ll check out this firmware updated, though.

Derrick – That link i gave you above is for multiple drives so if you have other SAS/SATA drives in other systems both newer or older then your current one it will work on that as well.

Chris – Excellent. I will try it out.

Derrick – Yea, there is no way to predict it, weve had some take years before problems occur and some only take a few weeks..

Chris – Gotta love that >:

Derrick – I’ll have that case for you in a moment, almost done with that..

Chris – No problem.

Chris – Case# 803471993

Derrick – Thanks for waiting, that took a bit longer then i expected.

Chris – Okay. No problem.

Derrick – So you should see that drive there tomorrow in the AM hours.

Derrick – Sounds good.

Chris – I’ll use this diagnostic tool as well.

Derrick – Other then that when you get a chance to reboot i would make sure to apply that firmware update for the drives, that will help out in the long run.

Chris – No problem.

Derrick – Other then that are you set for now?

Chris – Yessir.

Chris – Thanks for your help.