ZFS - Building, Testing, and Benchmarkingby Matt Breitbach on October 5, 2010 4:33 PM EST
- Posted in
- IT Computing
If you are in the IT field, you have no doubt heard a lot of great things about ZFS, the file system originally introduced by Sun in 2004. The ZFS file system has features that make it an exciting part of a solid SAN solution. For example, ZFS can use SSD drives to cache blocks of data. That ZFS feature is called the L2ARC. A ZFS file system is built on top of a storage pool made up of multiple devices. A ZFS file system can be shared through iSCSI, NFS, and CFS/SAMBA.
We need a lot of reliable storage to host low cost websites at No Support Linux Hosting. In the past, we have used Promise iSCSI solutions for SAN based storage. The Promise SAN solutions are reliable, but they tend to run out of disk IO long before they run out of disk space. As a result, we have been intentionally under-utilizing our current SAN boxes. We decided to investigate other storage options this year in an effort to improve the performance of our storage without letting costs get completely out of hand.
We decided to spend some time really getting to know OpenSolaris and ZFS. Our theory was that we could build a custom ZFS based server for roughly the same price as the Promise M610i SAN, and the ZFS based SAN could outperform the M610i at that price point. If our theory proved right, we would use the ZFS boxes in future deployments. We also tested the most popular OpenSolaris based storage solution, Nexenta, on the same hardware. We decided to blog about our findings and progress at ZFSBuild.com, so others could benefit from anything we learned throughout the project.
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diamondsw2 - Tuesday, October 5, 2010 - linkYou're not doing your readers any favors by conflating the terms NAS and SAN. NAS devices (such as what you've described here) are Network Attached Storage, accessed over Ethernet, and usually via fileshares (NFS, CIFS, even AFP) with file-level access. SAN is Storage Area Network, nearly always implemented with Fibre Channel, and offers block-level access. About the only gray area is that iSCSI allows block-level access to a NAS, but that doesn't magically turn it into a SAN with a storage fabric.
Honestly, given the problems I've seen with NAS devices and the burden a well-designed one will put on a switch backplane, I just don't see the point for anything outside the smallest installations where the storage is tied to a handful of servers. By the time you have a NAS set up *well* you're inevitably going to start taxing your switches, which leads to setting up dedicated storage switches, which means... you might as well have set up a real SAN with 8Gbps fibre channel and been done with it.
NAS is great for home use - no special hardware and cabling, and options as cheap as you want to go - but it's a pretty poor way to handle centralized storage in the datacenter.
cdillon - Tuesday, October 5, 2010 - linkThe terms NAS and SAN have become rightfully mixed, because modern storage appliances can do the jobs of both. Add some FC HBAs to the above ZFS storage system and create some FC Targets using Comstar in OpenSolaris or Nexenta and guess what? You've got a "SAN" box. Nexenta can even do active/active failover and everything else that makes it worthy of being called a true "Enterprise SAN" solution.
I like our FC SAN here, but holy cow is it expensive, and its not getting any cheaper as time goes on. I foresee iSCSI via plain 10G Ethernet and also FCoE (which is 10G Ethernet + FC sharing the same physical HBA and data link) completely taking over the Fibre Channel market within the next decade, which will only serve to completely erase the line between "NAS" and "SAN".
mbreitba - Tuesday, October 5, 2010 - linkThe systems as configured in this article are block level storage devices accessed over a gigabit network using iSCSI. I would strongly consider that a SAN device over a NAS device. Also, the storage network is segregated onto a separate network already, isolated from the primary network.
We also backed this device with 20Gbps InfiniBand, but had issues getting the IB network stable, so we did not include it in the article.
Maveric007 - Tuesday, October 5, 2010 - linkI find iscsi is closer to a NAS then a SAN to be honest. The performance difference between iscsi and san are much further away then iscsi and nas.
Mattbreitbach - Tuesday, October 5, 2010 - linkiSCSI is block based storage, NAS is file based. The transport used is irrelevent. We could use iSCSI over 10GbE, or over InfiniBand, which would increase the performance significantly, and probably exceed what is available on the most expensive 8Gb FC available.
mino - Tuesday, October 5, 2010 - linkYou are confusing the NAS vs. SAN terminology with the interconnects terminology and vice versa.
SAN, NAS, DAS ... are abstract methods how a data client accesses the stored data.
--Network Attached Storage (NAS), per definition, is an file/entity-based data storage solution.
- - - It is _usually_but_not_necessarily_ connected to a general-purpose data network
--Storage Area Network(SAN), per definition, is a block-access-based data storage solution.
- - - It is _usually_but_not_necessarily_THE_ dedicated data network.
Ethernet, FC, Infiniband, ... are physical data conduits, they are the ones who define in which PERFORMANCE class a solution belongs
iSCSI, SAS, FC, NFS, CIFS ... are logical conduits, they are the ones who define in which FEATURE CLASS a solution belongs
Today, most storage appliances allow for multiple ways to access the data, many of the simultaneously.
Calling a storage appliance, of whatever type, a "SAN" is pure jargon.
- It has nothing to do with the device "being" a SAN per se
Calling an appliance, of whatever type, a "NAS" means it is/will be used in the NAS role.
- It has nothing to do with the device "being" a NAS per se.
mkruer - Tuesday, October 5, 2010 - linkI think there needs to be a new term called SANNAS or snaz short for snazzy.
mmrezaie - Wednesday, October 6, 2010 - linkThanks, I learned a lot.
signal-lost - Friday, October 8, 2010 - linkDepends on the hardware sir.
My iSCSI Datacore SAN, pushes 20k iops for the same reason that their ZFS does it (Ram cacheing).
Fibre Channel SANs will always outperform iSCSI run over crappy switching.
Currently Fibre Channel maxes out at 8Gbps in most arrays. Even with MPIO, your better off with an iSCSI system and 10/40Gbps Ethernet if you do it right. Much cheaper, and you don't have to learn an entire new networking model (Fibre Channel or Infiniband).
MGSsancho - Tuesday, October 5, 2010 - linkwhile technically a SAN you can easily make it a NAS with a simple zfs set sharesmb=on as I am sure you are aware.