Well, trying to build an exhaustive list of topics to be covered for Data storage interview. So, here goes the list:
- Storage Networking. Why Storage networking?
- DAS, NAS, SAN. Advantages and disadvantages of these. Also, how does NAS overcome the limitations of DAS and similarly how does SAN overcome limitations of NAS? When and how to use one of these?
- Storage I/O stack. Components and function of each component?
- Storage devices
- Storage subsystems
- SCSI/SASI
- FCP
- iSCSI
- SAS
- SATA
- RAID, JBODs, HBAs
- Backup,restore
- Storage virtualization
- File systems
- Clustering
- Multipathing
- Distributed filesystems
- NFS
- CIFS
- NDMP
- Information Life Cycle Management
- Cloud Computing
Will keep adding to this post as and when I remember few more or come across some new ones :)
LVM-Part II
This post is dedicated to introduction to LVM(Wrote the first post and realized later that I missed the obvious stuff in the blog...)
LVM-Logical Volume Manager
- LVM provides a high-level view of the disk storage on a computer system.
- Provides the system administrator with a lot more flexibility in allocating storage to users/applications. It helps resizing/moving around the storage volumes(of course, the storage volumes, that are created under LVM's control)
- User-friendliness is another aspect, which can be talked about, in this context.Imagine, a situation, when the system administrator has to deal with the physical disk names such as "sda","sdb" etc.Instead, he can manage storage volumes in user-defines groups and also name them sensibly. Example: He could name volume groups as "Marketing", "HR", "Sales" etc to identify them easily.
Note: Every platform has its own native LVM and then there are third party Volume Managers like Veritas VxVM, that can be installed on the host machines.The LVM commands vary from one Volume Manager to another. Here is an easy reference guide:
http://www.unixguide.net/unixguide.shtml
Lets go through some common tasks that LVM can perform(Please be careful while repeating them on your system. Providing a wrong name of the partition could ruin your system-BE CAREFUL and know what are you doing)
The commands below belong to Linux LVM.
Initializing disks or disk partitions
--------------------------------------
To be continued...
LVM-Logical Volume Manager
- LVM provides a high-level view of the disk storage on a computer system.
- Provides the system administrator with a lot more flexibility in allocating storage to users/applications. It helps resizing/moving around the storage volumes(of course, the storage volumes, that are created under LVM's control)
- User-friendliness is another aspect, which can be talked about, in this context.Imagine, a situation, when the system administrator has to deal with the physical disk names such as "sda","sdb" etc.Instead, he can manage storage volumes in user-defines groups and also name them sensibly. Example: He could name volume groups as "Marketing", "HR", "Sales" etc to identify them easily.
Note: Every platform has its own native LVM and then there are third party Volume Managers like Veritas VxVM, that can be installed on the host machines.The LVM commands vary from one Volume Manager to another. Here is an easy reference guide:
http://www.unixguide.net/unixguide.shtml
Lets go through some common tasks that LVM can perform(Please be careful while repeating them on your system. Providing a wrong name of the partition could ruin your system-BE CAREFUL and know what are you doing)
The commands below belong to Linux LVM.
Initializing disks or disk partitions
--------------------------------------
To be continued...
LVM-Part I
This post and coming few posts will be dedicated to LVM and comparing various LVM commands across multiple UNIX OS flavors viz. AIX, HP-UX, Linux, Solaris ...
So lets start...Here's what does the abbreviation "LVM" stand for and what exactly is LVM?
LVM-Logical Volume Manager
Logical Volume Manager allows administrators to allocate storage to applications and users, in a flexible way.
The main elements of an LVM system are:
1. Volume Group(VG)
2. Physical Volume(PV)
3. Logical Volume(LV)
4. Physical Extent(PE)
5. Logical Extent(LE)
Here is how these elements fit in a system:
As per above diagram, here is how the actual system would look like(an example)
Click on the picture below, to have a closer n clearer look :)
So lets start...Here's what does the abbreviation "LVM" stand for and what exactly is LVM?
LVM-Logical Volume Manager
Logical Volume Manager allows administrators to allocate storage to applications and users, in a flexible way.
The main elements of an LVM system are:
1. Volume Group(VG)
2. Physical Volume(PV)
3. Logical Volume(LV)
4. Physical Extent(PE)
5. Logical Extent(LE)
Here is how these elements fit in a system:
As per above diagram, here is how the actual system would look like(an example)
Click on the picture below, to have a closer n clearer look :)
How to increase semaphore limit in Linux?
On Red Hat Linux, the default limit of 128 semaphore arrays can be increased to 1024 by adding line below to /etc/sysctl.conf:
kernel.sem=250 32000 32 1024 Use "ipcs -sl" to see the limits and "ipcs -s" to see the semaphores in use.
The user will need to run sysctl -p. NetApp 50% Virtualization Guarantee program
Quite interesting one ...
www.netapp.com/guarantee
Well, to summarize the above link, NetApp promises its customers that they will require 50% less storage, if they use NetApp products, compared to competition.
And the cool features that a customer can use, to enjoy a great solution are :
1. Snapshots
2. FlexVols
3. ThinProvisioning
4. Deduplication
5. RAID-DP
www.netapp.com/guarantee
Well, to summarize the above link, NetApp promises its customers that they will require 50% less storage, if they use NetApp products, compared to competition.
And the cool features that a customer can use, to enjoy a great solution are :
1. Snapshots
2. FlexVols
3. ThinProvisioning
4. Deduplication
5. RAID-DP
FCP LUNs not visible on the host!!!
Problem: You have mapped LUNs on a storage system to a host machine using FCP. Now the issue is that the LUNs are not being discovered on the host.
Solution:
See the checklist below:
Solution:
See the checklist below:
- HBA has the correct driver corresponding to the OS being used
- FC connectivity between the host and the storage system
- Host and the storage system belong to same zone in the FC switch
- LUNs on the storage system are mapped to the correct igroup(corresponding to the host, where you are trying to discover the LUNs
How to transport an installed rpm to another host?
Problem: An rpm package is installed on a host. Now the installable is missing and you need to install similar binary on another host.
Solution:
tar cvf /tmp/newpackage.tar $(rpm -ql packagename)
Then this package can be restored on the new host.
Solution:
tar cvf /tmp/newpackage.tar $(rpm -ql packagename)
Then this package can be restored on the new host.
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