Direct IO: Can be set to 0 or 1 where 0 uses the target system buffers and 1 sends the IOs directly to the disk.Ī couple of reserved keywords exists in fio and those will be replaced with the system values.Threads or processes: This represents the number of threads that the job will be spread upon.IO depth: if the IO engine is async, this represents how large is the queue depth for the incoming IO operations.It can be regular read/write operations, memory mapping the file, splice, async IO or SCSI generic operations via the SG driver in Linux kernel. IO size: Represents how much data is going to be written or read.In order to get close to the real application scenario, you can choose to use the block size that the application uses or a range of block sizes. Block size: This represents how large are the chunks for each IO issued.IO type: sequential read/write, random read/write, mixt read and write, random read and write.And the best tool to do that is fio.įio is the most complete tool for disk performance testing and it basically simulates a desired IO workload via a job that one or more threads and can contain quite a lot of parameters.Ī few of the most important parameters that can be used are: Soon you'll be interested in your disk performance. Let's say that the disk is now visible, you partition it, use it in a raid-group (and you'd better do that), schedule a backup policy for the newly created filesystem (you'd better do that too) and start using it. In the above command the hyphens stand for controller, channel, lun so "-" indicates that all controllers, channels, and luns are to be scanned. The next command can be used to rescan the bus:Įcho "-" > /sys/class/scsi_host/host6/scan sys/class/scsi_host/host6/proc_name:mpt2sas and host6 in this case is the bus number. Grep mpt /sys/class/scsi_host/host?/proc_name When no changes on the SCSI bus are seen or it takes a long time you can simply follow the next.įirst you must find your host bus number. If the SCSI Bus refresh works automatically, it usually can be seen in the system logs and it looks something like this. Sometimes when physically adding or removing a disk you get a proper delay from the Linux kernel in sensing the SCSI bus change. Let's first start with a little trick that helps you rescan the SCSI bus when adding or removing a disk from the system.
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