I encountered an intriguing issue recently after replacing my motherboard. Some block devices underwent a change in their order, causing /dev/sda to appear as /dev/sdy due to a modification in the PCI-e enumeration. This change, though seemingly insignificant, led to an unexpected consequence. Since the disk was subject to a specific mdadm filter, its altered…
The IO scheduler blk_mq was designed to increase disk performance – better IOps and lower latency – on flash disk systems, with emphasis on NVME devices. A nice by-product, is that it increases performance on the “older” SCSI/SAS/SATA layer as well, when the disks in the back are SSD, and even when they are rotational…
While searching the web for how to perform PCI-Passthrough on XenServers, we mostly get info about previous versions. Since I have just completed setting up PCI-Passthrough on XenServer version 6. 5 (with recent update 8, just to give you some notion of the exact time frame), I am sharing it here. Hardware: Cisco UCS blades,…
When Connecting Linux to a large array of SAS disks (JBOD), udev creates default persistent names in /dev/disk/by-* . These names are based on LUN ID (all disks take lun0 by default), and by path, which includes, for a pure SAS bus – the PWWN of the disks. It means that an example to such…
I have demonstrated how to hot-add LUNs to a Linux system with Qlogic HBA. This has become irrelevant with the newer method, available for RHEL4 Update 3 and above. The new method is as follow: echo 1 > /sys/class/fc_host/host/issue_lip echo “- – -” > /sys/class/scsi_host/host/scan< Replace "<ID>" with your relevant HBA ID. Notice - due...
Setting up an Oracle ASM disks is rather simple, and the procedure can be easily obtained from here, for example. This is nice and pretty, and works well for most environments. EMC PowerPath creates meta devices which utilize the underlying paths, as mod_scsi sees them in Linux, without hiding them (unlike IBM’s RDAC, for example)….
