1) What is Raid and Raid Level
RAID can allow for better storage performance and higher availability, and there are many different RAID types.
RAID (originally redundant array of inexpensive disks; now commonly redundant array of independent disks) is a data storage virtualization technology that combines multiple disk drive components into a logical unit for the purposes of data redundancy or performance improvement.
Raid contains groups or sets or Arrays. A combine of drivers make a group of disks to form a RAID Array or RAID set. It can be a minimum of 2 number of disk connected to a raid controller and make a logical volume or more drives can be in a group. Only one Raid level can be applied in a group of disks. Raid are used when we need excellent performance. According to our selected raid level, performance will differ. Saving our data by fault tolerance & high availability.
In RAID we have different RAID levels
1. Level 0 - striped disk array without fault tolerance
2. Level 1 - mirroring and duplexing
3. Level 2 - error-correcting coding
4. Level 3 - bit-interleaved parity
5. Level 4 - dedicated parity drive
6. Level 5 - block interleaved distributed parity
7. Level 6 - independent data disks with double parity
8. Level 10 - a stripe of mirrors
In RAID we have different RAID levels
1. Level 0 - striped disk array without fault tolerance
2. Level 1 - mirroring and duplexing
3. Level 2 - error-correcting coding
4. Level 3 - bit-interleaved parity
5. Level 4 - dedicated parity drive
6. Level 5 - block interleaved distributed parity
7. Level 6 - independent data disks with double parity
8. Level 10 - a stripe of mirrors
2) Difference Between Raid 5 and Raid 1 + 0
RAID Level 5: Block-level striping with distributed parity. Each entire data block is written on a data disk; parity for blocks in the same rank is generated on Writes, recorded in a distributed location and checked on Reads. Requires minimum 3 disks to implement
·
- Highest Read data transaction rate
- Medium Write data transaction rate
- Low ratio of ECC (Parity) disks to data disks means high efficiency
- Good aggregate transfer rate
RAID Level 0: It’s just stripping. RAID Level 0 requires a minimum of 2 drives to implement.
RAID Level 1: For Highest performance, the controller must be able to perform two concurrent separate Reads per mirrored pair or two duplicate Writes per mirrored pair. Raid level 1 requires a minimum of 2 drives to implement.
3) what is differene between Hardware Raid and Software Raid.
- RAID 0 implements a striped disk array, the data is broken down into blocks and each block is written to a separate disk drive
- I/O performance is greatly improved by spreading the I/O load across many channels and drives
- Best performance is achieved when data is striped across multiple controllers with only one drive per controller
- No parity calculation overhead is involved
- Very simple design
- Easy to implement
- One Write or two Reads possible per mirrored pair
- Twice the Read transaction rate of single disks, same Write transaction rate as single disks
- 100% redundancy of data means no rebuild is necessary in case of a disk failure, just a copy to the replacement disk
- Transfer rate per block is equal to that of a single disk
- Under certain circumstances, RAID 1 can sustain multiple simultaneous drive failures
- Simplest RAID storage subsystem design
Implementing the RAID will be two types 1.Software RAID and 2.Hardware RAID
Let’s see the difference between those
Let’s see the difference between those
SOFTWARE RAID
|
HARDWARE RAID
|
| 1. It will use computer system CPU | 1. It will use its own CPU |
| 2. Low cost compare to H/W RAID | 2.More cost compare to S/W RAID |
| 3. It has data integrity issues due to system crashes |
3.No data integrity issues
|
| 4. No write-back cache | 4.It is capable of write-back cache |
| 5. Limited operating system migrations | 5.Can be migrated to any OS type |
| 6. Unprotected at boot (cannot manage or protect data at boot):Drive failure or corrupted data during boot and before the RAID software become active leads to an inoperable system | 6. Protected at boot: No negative impact on data availability when boot drive has medium errors or fails completely |
| 7. Performance issues will be there | 7.No performance issues compare to S/W RAID |
Hardware RAID have high performance. They are dedicated RAID Controller which is Physically built using PCI express cards. It won’t use the host resource. They have NVRAM for cache to read and write. Stores cache while rebuild even if there is power-failure, it will store the cache using battery power backups. Very costly investments needed for a large scale.
4) Why FTP work on 21 port?
Reserved TCP port used by File Transfer Protocol (FTP) to initiate and control connections to FTP servers.
Description:
To establish an FTP session, clients initiate a connection to an FTP server that listens on TCP port 21 by default. FTP servers respond with messages that prompt the client for FTP login credentials (username and password). FTP servers do not, however, send files from port number 21.
Instead, the FTP protocol allows for a second connection to be established for data transfer after the control connection is established. Note that only FTP servers use port 21, not FTP clients.
NFS –Network File Sharing
NFS PORT ------2049
NFS Run on UDP Protocol
NFS doesn’t ask to username & password
NFS used for Linux to Linux only
NFS fast and good performance
Starting NFS quotas: -------ok ]
Starting NFS deamon: ------ok ] Child Service
Starting NFS mountd: ------ok ]
exportfs –v ------ Display
*(sync) ------- * means ----sharing to all network
showmount -e 192.168.10.x ------ to check it out share drive is accessible or not
6) DNS configuration file name
DNS Package name : bind*
Ext4
8) Boot Process.
9) If Server Load Increase What is Troubleshooting steps you will follow.
High server load – What is it really?
10) Command SAR
SAR System Monitoring
12) How DHCP works (DORA Process)
DHCP stands for Dynamic Host Configuration Protocol.
The DORA process in DHCP works as folows.
3) In response to the offer Client requests the server.
4)Server responds all the Ip Add/mask/gty/dns/wins info along with the acknowledgement packet.
13) Subversion
NFS V3 VS NFS V4
Export Management
- In NFSv3, client must rely on auxiliary protocol, the mount protocol to request a list of server’s exports and obtain root filehandle of a given export. It is fed into the NFS protocol proper once the root filehandle is obtained.
- In NFSv4 uses the virtual file system to present the server’s export and associated root filehandles to the client.
- NFSv4 defines a special operation to retrieve the Root filehandle and the NFS Server presents the appearance to the client that each export is just a directory in the pseudofs
- NFSv4 Pseudo File System is supposed to provide maximum flexibility. Exports Path name on servers can be changed transparently to clients.
/etc/named.conf
DNS Package name : bind*
DNS Port : 53
- Ext4 stands for fourth extended file system.
- It was introduced in 2008.
- Starting from Linux Kernel 2.6.19 ext4 was available.
- Supports huge individual file size and overall file system size.
- Maximum individual file size can be from 16 GB to 16 TB
- Overall maximum ext4 file system size is 1 EB (exabyte). 1 EB = 1024 PB (petabyte). 1 PB = 1024 TB (terabyte).
- Directory can contain a maximum of 64,000 subdirectories (as opposed to 32,000 in ext3)
- You can also mount an existing ext3 fs as ext4 fs (without having to upgrade it).
- Several other new features are introduced in ext4: multiblock allocation, delayed allocation, journal checksum. fast fsck, etc. All you need to know is that these new features have improved the performance and reliability of the filesystem when compared to ext3.
- In ext4, you also have the option of turning the journaling feature “off”.
- The XFS file system is an extension of the extent file system.
- The XFS is a high-performance 64-bit journaling file system.
- The support of the XFS was merged into Linux kernel in around 2002 and In 2009 Red Hat Enterprise Linux version 5.4 usage of the XFS file system.
- XFS supports maximum file system size of 8 exbibytes for the 64-bit file system.
- There is some comparison of XFS file system is XFS file system can’t be shrunk and poor performance with deletions of the large numbers of files.
- Now, the RHEL 7.0 uses XFS as the default filesystem.
Common Commands for ext3 and ext4 Compared to XFS
| Task | ext3/4 | XFS |
|---|---|---|
| Create a file system | mkfs.ext4 or mkfs.ext3 | mkfs.xfs |
| File system check | e2fsck | xfs_repair |
| Resizing a file system | resize2fs | xfs_growfs |
| Save an image of a file system | e2image | xfs_metadump and xfs_mdrestore |
| Label or tune a file system | tune2fs | xfs_admin |
| Backup a file system | dump and restore | xfsdump and xfsrestore |
8) Boot Process.
The following are the 6 high level stages of a typical Linux boot process.
A server functions with a limited set of resources. For eg., an average server these days will have 8 GB RAM, 4 processors, 75 IOPS SATA II hard disks, and 1 Gigabit NIC cards.
Now, let’s assume one user decided to backup their account. If that process occupies 7.5 GB of RAM, other users or services in the system have to wait for that process to get over. The longer the backup takes, the longer the wait queue. The “length” of the queue is represented as server load. So, a server running at load avg. 20, will have a longer wait queue than a server at load avg. 10.
When you get a high load notification, there’s only one thing you know. That is – there’s some server resource (RAM, CPU, I/O, etc.) that’s being abused.
So, the first step is to find out which resource is being abused. The next step is to find out which service is using that resource. It could be the web server, database server, mail server, or some other service. Once you have the service, you can then find out which user in that service is actually abusing the server.
The key to quickly trace a load spike is to go from what you know to what you don’t.
When you get a high load notification, there’s only one thing you know. That is – there’s some server resource (RAM, CPU, I/O, etc.) that’s being abused.
- Find the over-loaded resource
- Find the service hogging that resource
- Find the virtual host over-using that service
DHCP stands for Dynamic Host Configuration Protocol.
The DORA process in DHCP works as folows.
D ----------> Discover
O ----------> Offer
R ----------> Request
A ----------> Acknowledgement
D – D in the term DORA stands for the DHCP Discover packet. The DHCP Discover packet
is broadcasted by the DHCP client computer in order to find the available DHCP server(s) in the network. Since the DHCP client computer sends the DHCP Discover packet as a broadcast, all the
DHCP servers that are present in the network receive the packet and respond accordingly.
O – O in the term DORA stands for the DHCP Offer packet. The DHCP Offer is a unicast packet that is sent by the DHCP server who receives the DHCP Discover packet from the DHCP client computer. The DHCP Offer packet contains the available IP address that the DHCP server offers to the client computer.
R – R in the term DORA stands for the DHCP Request packet. The DHCP Request is again a unicast packet sent by the DHCP client computer to the DHCP server who had sent the DHCP Offer packet to the client computer. With the help of the DHCP Request packet, the DHCP client computer requests the DHCP server to assign the offered IP address to it.
O ----------> Offer
R ----------> Request
A ----------> Acknowledgement
DHCP (D)iscover | DHCP (O)ffer | DHCP (R)equest | DHCP (A)ck
D – D in the term DORA stands for the DHCP Discover packet. The DHCP Discover packet
is broadcasted by the DHCP client computer in order to find the available DHCP server(s) in the network. Since the DHCP client computer sends the DHCP Discover packet as a broadcast, all the
DHCP servers that are present in the network receive the packet and respond accordingly.
O – O in the term DORA stands for the DHCP Offer packet. The DHCP Offer is a unicast packet that is sent by the DHCP server who receives the DHCP Discover packet from the DHCP client computer. The DHCP Offer packet contains the available IP address that the DHCP server offers to the client computer.
R – R in the term DORA stands for the DHCP Request packet. The DHCP Request is again a unicast packet sent by the DHCP client computer to the DHCP server who had sent the DHCP Offer packet to the client computer. With the help of the DHCP Request packet, the DHCP client computer requests the DHCP server to assign the offered IP address to it.
A – A in the term DORA stands for the DHCP Acknowledge packet. The DHCP Acknowledge is a unicast packet sent by the DHCP server to the DHCP client computer acknowledging the assignment of the offered IP address for a specific lease time.
1) Client makes a UDP Broadcast to the server about the DHCP discovery.
2) DHCP offers to the client.3) In response to the offer Client requests the server.
4)Server responds all the Ip Add/mask/gty/dns/wins info along with the acknowledgement packet.
