Category Archives: storage

Disk Read-Ahead in Linux

TweetWe 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

TweetWe 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

TweetWe 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 »

>Software RAID vs Fake RAID

Tweet> Many of us already very much aware of Hardware and Software RAID. Keeping performance in mind , hardware RAID is always preferable over software RAID but budget become constraint sometimes. Generally we use software RAID to save the cost of hardware RAID. Why Hardware RAID are costlier than software RAID ? The answer is… Read More »

>Reclaim Storage Space in Ext4

Tweet> One of the excellent feature supported by Ext3 and Ext4 filesystem, is reclaiming the free space. On many occasions it become very difficult to convert the freed storage space into the reusable storage space. The storage space freed by the applications or the databases may remain marked as engaged space. Storage admins always wish for a… Read More »

>Multipathing

Tweet> Multipathing allow access to storage device via more than one path. Without going in internals of multipathing on Linux environment, here I am trying to explain basic functionality of multipathing by an example. On my testing CentOS 6 testing machine , issuing multipath -l command showing following output  In the above given output of multipath -l command,… Read More »

>Bad Sector on Hard Disk

Tweet> Modern disk map bad sector to good sector to avoid any sort of error due to bad sector. If a large number of sector mapped to another sectors that means disk is going to fail smartctl command is very helpful command to diagnose disk related problems To instruct for selftest , we can issue following… Read More »

>FDISK vs CFDISK vs SFDISK

Tweet>As we know fdisk,sfdisk and cfdisk all these are disk manipulator command. cfdisk is almost same as fdisk but graphical based because it use ncurse. If someone is not a system admin he should prefer cfdisk over fdisk. According to fdisk man page. sfdisk is for hackers only – the userinterface is terrible, but it… Read More »

>RAID 1 on IDE disk

Tweet>If we use IDE disk in RAID 1 then we need to restart system when one of disk become faulty. Suppose a raid device /dev/md0 exist that consist two ide disk /dev/sda and /dev/sdb and we set one of disk as fault #mdadm mdadm /dev/md0 -f /dev/hda1 And followed by removing disk from raid array#mdadm /dev/md0… Read More »