Details of the talk I’ll be giving at the upcoming LinuxWorld in Toronto, Canada: http://www.lwnwexpo.plumcom.ca/session_detail.cfm?id=239
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Xsan: Zoning and Metadata
Only the MDCs are required to see the Metadata LUN. The rest of the clients receive the extents from the MDCs to write to the “data” LUNs. Yes the clients need to see the Data LUNs, but clients do not need to see Metadata LUNs. Before you can upgrade a client to an MDC though, verify that you can see the Metadata LUNs if you are zoning this way. It’s the most secure way but requires a little extra zoning.
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Xsan: Fragmentation
Xsan volumes can get fragmented. This can cause the performance to move to a grinding halt. Dropped frames, slow copy times, even volume corruption are common side effects. So, to defrag the volume you can use snfsdefrag. This command-line tool will defrag volumes or files. You can even specify what to do with the fragmented data, giving you a way to move data between storage pools…
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Xsan: Multiple Volumes
In Xsan 1.x you can have multiple volumes. Each will consist of a given number of Storage Groups that in turn consist of a given number of LUNs, as we’ve described in the past. If you have multiple volumes then they will all use the same Metadata Controllers. Each additional volume will also need its own dedicated Metadata LUN. Therefore, if you have 4 volumes, with 4 LUNs of data storage in each volume then you will have a total of 16 LUNs for data and another 4 for metadata to total out 20 LUNs. Essentially by splitting it up this way you are loosing 4 LUNs (up to 20TB…
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Xsan: Affinity
cvaffinity can be used to assign an affinity to a storage pool in Xsan. An affinity maps a specified directory to a storage pool. Therefore, if you have a dedicated capture station and you want to make sure it always has 4gbps of throughput then you can create a storage pool called capture, mark it for use with affinity only, create a folder called capture and assign the affinity for the capture storage pool to the capture folder on the volume. Now all data written to that folder will be written through the affinity and therefore provide a certain level of Quality of Service to that affinity.
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Xsan: Storage Pools
Earlier, we described a LUN. In Xsan you can take multiple LUNs and stream data to them in a round-robin fashion. When doing so you will group them together in what Xsan calls Storage Pools. Each Storage Pool has a maximum throughput of about 4 LUNs worth of storage. Each of the LUNs (in Xsan 1.0) has a maximum of about 2TB in capacity. Therefore each Storage Pool can typically net you around 4gbps of speed and about 8TB in capacity. You can then lump multiple Storage Pools into a given Volume to obtain volume sizes of 32, 40, 48, etc. TB. However, when you do so you will not…
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Installing Xsan 1.x
You will install the xSAN software on all of the systems that will be running as Metadata Controllers and on all of the client computers. To install the xSAN software: Run the Install Xsan.mpkg file from the Xsan Install Disc. Read the Welcome to the Xsan Installer screen and click Continue. Read the Important Information and click Continue. Read the Software License Agreement and click Continue. Agree to the Software License Agreement by clicking on the Agree button. Select the volume for the Xsan software to be installed on. Once your Destination has been selected, click Continue (see Figure 2.x). Figure 2.x Select a Destination If you would like to…
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Xsan: LUN
An Xserve RAID can be split into multiple logical units, referred to as a LUN. Each side, or channel, of the RAID is, by default a single LUN. You can use the RAID Admin utility (located at /Applications/Server) to format each of these as multiple LUNs if you wish. When the LUNs are formatting (which generally takes 48 hours) you will start to see them in disk utility. Do not assign a file system to them yet if you are to use them with Xsan. Instead you will use the cvlabel command to label each of your LUNs, which marks them as able to be used by Xsan.
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Xsan: What is Fiber Channel
Fiber Channel is a technology for transmitting data between computer devices similar to SCSI but with networking components based on fiber optics. Fiber Channel is especially suited for attaching computer servers to shared storage devices and for interconnecting storage controllers and drives. Apple uses Fiber Channel for Xsan, it’s storage virtualization platform. All of the objects that make up a Fiber Channel network are referred to as the fabric. These typically include HBAs (the card that goes in a machine), cabling, transceivers, a fiber channel switch and the fiber channel controllers on the storage.
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Xserve RAID: Reset Controller
Unmount any Xserve RAID volumes hosted by the RAID (especially Xsan volumes). Press the reset button on the back of the controller module for about ten seconds. You should see the controller restart and then the controller should be reset. Sometimes you need to reset both controllers. You don’t have to reset the whole controller to just reset the password. To do that, you can press the reset button for about 1-2 seconds and then try to authenticate through RAID Admin to reset the password. By default the password to view the Xserve RAID, once reset is public and to edit settings, the default password is private. By default the IP…