I want to append new data in a file stored in SSD. dd if=/dev/shm/test of=/data/sdb/test bs=1G oflag=append But df -h shows the dd command always overwrite the test file, instead appends new data in the test file. I also tried dd if=/dev/shm/test of=/data/sdb/test bs=1G conv=notrunc It does not work, either. Solution: What about: dd if=/dev/shm/test…
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What is Termination?Cables make up the physical connections of the SCSI bus. Since the SCSI bus is a chain of devices on a cable rather than a loop, the two ends of the bus must be terminated. Every wire in the cable has a specific impedance, or resistance to the passing of electrical signals. When signals reach the end of the cable that makes up the SCSI bus, they encounter the air, which has very high impedance and acts as a wall of infinite resistance. The problem with high impedance is that any signal coming down the bus is reflected back in the other direction once it hits this barrier. Terminating both ends of the cable prevents the signal from being reflected.
You terminate the bus by attaching a circuit, the terminator, to the physical ends of the SCSI bus. The terminator provides an impedance that matches the cable’s, thereby preventing the signal from bouncing back. The terminators use power, and the power to operate them comes from the SCSI interface card through the termination power wire on the bus.
Passive Termination is the oldest method of termination, defined in the specs for SCSI-1. Basically, a passive terminator sits on the bus to minimize reflections at the end of the cable. The terminator doesn’t really do any work to regulate power for termination; it relies on the interface card to provide steady power. A passive terminator simply provides impedance that’s close to the impedance of the cable.
Active termination works to control the impedance at the end of the SCSI bus by using a voltage regulator, not just the power supplied by the interface card. Because it is active, regulating the power that it gets from the interface card, active termination is more stable than passive termination.
Forced perfect termination is the most complex of the terminators, going beyond merely stabilizing the power applied to the terminator. It can actually alter its impedance to compensate for variations in impedance among many different cables, devices, and terminators. It is usually used in high-speed SCSI systems that have many different devices, cables, and terminator types. The complexity of such a system can cause impedance mismatches that degrade the signals sent through the bus. FPT actively compensates for these impedance variations by means of diode switching and biasing to force the impedance of the cable to match each device.
If you are installing a Seagate drive in a system that has other SCSI devices installed, terminate only the end devices on the SCSI chain. A SCSI “device” is any disc drive, scanner, tape backup unit, or other piece of hardware connected to your system using the SCSI bus.
The example above shows an internal hard disc at one end of the SCSI bus with the SCSI controller at the other end (both are terminated). The bottom example shows two additional SCSI devices connected externally-this means the SCSI controller is no longer on the end of the SCSI chain and should not be terminated.
Note: Some controllers prefer to remain terminated even if they are in the middle of the chain. Also, some controllers treat the internal and external chains as separate logical buses. This means you may need to terminate both the first and last devices on both logical buses to achieve proper termination. If necessary, refer to your system or controller documentation to see how this is handled in your particular system.
Slide 4500: Doing a Platter Swap for a Single Platter
List of items needed:
The first step is to get a hard drive as close to identical as the bad drive you have that is a working drive. At the bottom of this paper you will find help about matching hard drives and serial numbers.
You need a clean area to work on with as little dust floating around as possible.
You will need about 1 hour to do this carefully
A screwdriver set with T3-T8. These are my favorite http://www.wihatools.com/200seri/278serie.htm
Post-it Notes
Other tools depending on the drive
Anti-Static Gloves ($5 at the local store)
Patience
Just move the head as careful as you can to get it out of the way
NOTE:
This is a fairly simple task compared to a head swap. The hardest part is again getting the heads aligned and back on the platter correctly.
If you have a ramp on your drive it is fairly simple to get the head moved out of the way enough to get the platter in position.
Remove the platter from the good drive.
NOTE:
I usually will try to put a screwdriver in the shaft just to the edge of the center of the platter and turn the drive just enough to get the platter to slide on to the screw driver. I will do the same for the bad drive to move the platter to the good drive.
The platter will most likely never be used again so just get it out however you can without affecting the rest of the drive.
Again I use the Post-it notes in the shape of a V to get the heads back on the platter as I did in the head replacement.
Be very careful to keep the orientation in the same direction to so that the platter will be in the correct location when you put the platter back on the new drive.
Slide TBD: Doing a Platter Swap for a Multi-Platter
In order to do a Multi-Platter replacement you will need a special tool. If you have more than one platter and you take out the platters and any one of them turns at all, you will never get them aligned again or be able to read the data. This is because the data is written in a cylinder. Since the data is in a cylinder you must have the exact same alignment of the platters in order to move them to a new hard drive.
There is a special tool called a Platter Replacement Stand. You can get one at SalvationData.com http://www.salvationdata.com for around $250 plus postage. It is a really heavy stand and weighs about 10 pounds. The platter replacement tool is what you really need and it looks a lot like a coffee can with a slit in the side. Once you have moved your heads out of the way, this can sits down around all the platters and you can push down on a piece of metal mounted in the slit to tighten it around the platters. It also has a lid inside that sits on the top ring of the platters that will hold the screws and keep them from rolling around all over the platters.
The pressure from the “coffee can” will hold all the platters together; however you still have to be really careful about taking it out and turning it. It should go straight from one hard drive to the other as quickly as possible with as little movement as possible.
This is the best possible way to keep the drive platters lined up.
You will still reassemble the drive just like you do in a head stack replacement or a single platter replacement. The only difference is using this device to move the platters.
The plate inside the tool holds the screws so that they do not scratch the platter.
Realign the heads.
External hard drives are ideal for backing up your hard drive or storing additional media separately from your main hard drive. Photos, videos, and digital music have all become so popular in recent years that people need a place to put it all. CDs and DVDs do not have the capacity to hold PC backups and are not all that convenient. However, the prices of external hard drives have come down so much that they are perfect for backing up your important data.
The two most common interfaces for hooking up external drives to your computer are USB and FireWire with eSata now becoming popular also. USB has been around for years and are standard on just about all computers today while FireWire ports are newer and if you use a digital video camera with your computer you probably already have one. In terms of access speeds the latest eSata standard offers the fastest connection however that comes with a price. USB 2.0 and Firewire can cover most of your general needs without having to upgrade your system with a new eSata card. Any of the interfaces will do the job however be sure to purchase an external hard drive with the same type of port that your computer has.
WD Elements 640 GB USB 2.0 Portable External Hard Drive
Seagate FreeAgent Go 500 GB USB 2.0 Portable External Hard Drive
Iomega Prestige 1 TB USB 2.0 Desktop External Hard Drive
Toshiba 500 GB USB 2.0 Portable External Hard Drive
WD Elements 1.5 TB USB 2.0 Desktop External Hard Drive
Toshiba 320 GB USB 2.0 Portable External Hard Drive
WD Elements 1 TB USB 2.0 Desktop External Hard Drive
WD My Passport Essential SE 1 TB USB 2.0 Portable External Hard Drive
WD My DVR Expander 1 TB eSATA Desktop External Hard Drive
LaCie d2 Quadra Hard Disk 1 TB USB 2.0/FireWire 400/800/eSATA Desktop External Hard Drive
Seagate FreeAgent Go 500 GB USB 2.0 Portable External Hard Drive
Seagate Expansion 500 GB USB 2.0 Portable External Hard Drive
Iomega eGo Mac Edition 500 GB USB 2.0/FireWire 400/800 Portable External Hard Drive
Iomega Prestige 1.5 TB USB 2.0 Desktop External Hard Drive
Seagate Expansion 1 TB USB 2.0 Desktop External Hard Drive
Iomega Prestige 320 GB USB 2.0 Portable External Hard Drive
Iomega Prestige 500 GB USB 2.0 Desktop External Hard Drive
Seagate FreeAgent Go 250 GB USB 2.0 Portable External Hard Drive
Seagate Expansion 250 GB USB 2.0 Portable External Hard Drive
WD Elements 500 GB USB 2.0 Portable External Hard Drive
Note: Your backup drive should have a capacity at least as big as your computer’s largest hard drive. That will leave you with plenty of room to back up your important files or mirror/clone your current drive. You can also buy an external hard drive case and mount an internal hard drive inside it. This method will give you a choice of brands and models, and if anything goes wrong with your internal hard drive, you can simply install the external one inside your computer to replace it.
Case:The customer was modifying the website, and when the data was uploaded, the website suddenly found that the website could not be opened.I thought it was the machine room restarted the server.After a few minutes, I couldn’t open it.The staff of the computer room did not do it at all. Instead, the server was attacked,…
There are two different types of disk storage available to the Windows Vista, XP and 2000 environment:
The number of partitions (on basic disks) and volumes (on dynamic disks) that each can contain are the primary differences. Single drive systems with one drive letter C: are typical basic disks. A server that needs to be divided up into several parts may benefit from a dynamic disk configuration. Some versions of Windows will convert a basic disk into a dynamic type.
Basic Disk Storage
Basic storage uses partition tables that are supported by MS-DOS, Microsoft Windows 95, Microsoft Windows 98, Microsoft Windows Millennium Edition (Me), Microsoft Windows NT, Microsoft Windows 2000, and Windows XP. A disk initialized for basic storage is called a basic disk. A basic disk contains basic volumes, such as primary partitions, extended partitions, and logical drives.
Dynamic Disk Storage
Dynamic storage is supported by both Windows 2000 and Windows XP Professional. A disk that is initialized for dynamic storage is called a dynamic disk. A dynamic disk contains dynamic volumes, such as simple volumes, spanned volumes, striped volumes, mirrored volumes, and RAID-5 volumes.
The Windows Vista Recovery Environment can be useful in restoring system files affecting startup.
To use this feature:
1. Boot from the Vista Boot DVD
2. scroll through to choose a recovery tool
3. Statup repair can replace or repair corrupted system files. This is the first option shown
If startup repair is not able to resolve the issue and allow you to boot into Windows you will see the a dialogue window explaining that the repair was not successful along with problem details.
At this point you should contact your IT Admin or call tech support.
