Then click on the “Add Volume” to finish the volume creation. Log device: requires at least one dedicated device, a fast, low-latency, power-protected SSD is recommendedĬache device: requires at least one dedicated device, SSD is recommended Volume Manager only allows choosing a configuration if enough disks have been selected to create that configuration. Use drag and drop option/add button “+” to add the multiple disks to the volume. And you can see a list of available disks, Here I have three disks with size 21.5GB. Navigate to Storage > volumes > volume manager, Then give a name for Volume. Once logged in to FreeNAS web console navigate to services > Enable ISCSI service “start on boot” > click “start now” to start the service Here we are creating iSCSI storage software SAN with the help of FreeNAS v.11 and connecting to ESXi 6.5 by using Software iSCSI Adapter. You can set up VMFS datastores on any SCSI-based storage devices that the host discovers, including Fibre Channel, iSCSI, and local storage devices. To ensure that the same virtual machine is not accessed by multiple servers at the same time, VMFS provides on-disk locking. As a cluster file system, VMFS lets multiple ESXi hosts access the same VMFS datastore concurrently. iSCSI gets really fun with ZFS.Sharing the same VMFS volume across multiple hosts offers the following advantages: VMotion, HA, FT, DRS, SDRS etc, VMFS datastores serve as repositories for virtual machines. You probably want a large blocksize for compression to work more effectively, but that will have performance impacts for updating single 512-byte sectors of a virtual disk created on top of the zvol because the zvol will have to read a block, decompress it to a 128K chunk, do the update, then recompress the 128K chunk and chuck it back out to the pool. Under the hood, though, when ZFS is pushing blocks to and from the pool, it'll take care of the compression and decompression of the blocks transparently.ĭo note that there's some interesting implications in here. So this translates very directly to your question: how does a zvol work? And the answer is: "really easily." The zvol is not particularly aware of or involved in the compression it looks like and thinks that it is just a standard volume. So the compression ratio may be less than the file-based gzip, but it is totally transparent to the user. In a normal gzip-on-a-file run, the compression dictionary is potentially built over the set of the entire file contents, right? But ZFS cannot do that, because you might want to modify the blocks in the middle of the file. That number may not be as attractive as the per-file compression ratio. So for compressible data, perhaps your blocks can be compressed down to an average of 32KB. if a smaller blocksize can be used to store the data, then ZFS does. However, with compression, it could be less. Without compression, each one would be 128KB. So your file gets transformed into 16 blocks. Instead, your file is broken up into ZFS blocks. You're used to running "gzip" on the whole thing and having it end up as 200KB. Let's pretend you have a highly compressible file, two megabytes long. Then read these words: ZFS uses a variable block size. Compression for zvols works the same way as for the rest of the pool: it probably doesn't work the way you think it does.
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