Sysstat Package # sar

We recall while working on a production server, It was new for me to know that the great utility ‘sar’ is not only for historical (greatly used for this purpose) but also so good for fetching us real time “system activity data”. The greatness lies in the historical data collection capability though. As for live… Read More »

Ceph Basics

You might have heard  much about commercial storage solution which provides fault-tolerant. What about if you get such storage solution on open source platform? Ceph is fault-tolerant distributed clustered file system.  It’s not just a simple filesystem. It’s a filesystem, and a striped/replicated block device provider, and a virtualization storage backend, and a cloud object… Read More »

LVM Cache

LVM labels and volume group (VG) metadata stored inside physical volume. On Linux system startup vgscan command scan block devices of system and looking for LVM lables. Physical Volume(PV) scanned and Volume Group(VG) list prepared from VG metadata stored in PV. Name of Physical Volumes are stored in /etc/lvm/.cache, subsequent command read /etc/lvm/.cache instead of… Read More »

ReSize Disk Partition in Linux

Resizing disk is a very hot topic of discussion among the system administrators. A few admins agree and many disagree with the idea of resizing disk partitions. I am sharing my piece of knowledge on this. I have been in a situation where /tmp partition of disk has to be resized. My disk was of… Read More »

Missing PVs

I have a situation where LVM raid 1 is mirror is configured using two physical volume /dev/sdc1 and /dev/sdd1. Here /dev/sdc1 is a local disk and /dev/sdd1 is iscsi block device. Due to some reasons iscsi block device /dev/sdd1 went down. I brought iscsi block device (/dev/sdd1) up, so both physical volumes are available now… Read More »

Disk Read-Ahead in Linux

We know that Input Output process on disk is always a time consuming process. A number of ideas has been applied to improve I/O performance on disk and Read-Ahead is of the those ideas. Read-Ahead speeds up file access (Read operation on disk) by pre-fetching  data and loading it into RAM. The assumption is that… Read More »

RAID5 Parity

We know RAID0 is stripping and RAID5 is stripping with parity. Calculation of parity is a CPU intensive process. RAID5 does block level stripping with distributed parity. Let me explain what does mean by “Block level stripping with distributed parity”. Adding parity adds extra data and therefore requires storage space to store it. Here the… Read More »

Adding SAN storage path

We know adding the local disk to the system is a very simple task. Adding local disk appears in output of fdisk -l command and logfile /var/log/messages. This article is for the situation where Storage Server is Fibre Channel, I mean you need to use disk(LUN) available through SAN. In the case of Fibre Channel… Read More »

LVM online shrinking

Many Linux system administrators have wrong assumption that LVM does not support online shrinking. Fact is reverse of that, Linux LVM fully support online device shrink. But yes we know that when we need to shrink LVM device we unmount the subjected device. The reason to bring device in unmounted state before shrink lies in… Read More »