Instruct: Given a question, retrieve passages that answer the question.
Query: What is a data migration?
Data migration is the process of selecting, preparing, extracting, and transforming data and permanently transferring it from one computer storage system to another. Additionally, the validation of migrated data for completeness and the decommissioning of legacy data storage are considered part of the entire data migration process.[1][2] Data migration is a key consideration for any system implementation, upgrade, or consolidation, and it is typically performed in such a way as to be as automated as possible, freeing up human resources from tedious tasks. Data migration occurs for a variety of reasons, including server or storage equipment replacements, maintenance or upgrades, application migration, website consolidation, disaster recovery, and data center relocation.[2]
Planning: The data, applications, etc. that will be migrated are selected based on business, project, and technical requirements and dependencies. Hardware and bandwidth requirements are analyzed. Feasible migration and back-out scenarios are developed, as well as the associated tests, automation scripts, mappings, and procedures. Data cleansing and transformation requirements are also gauged for data formats to improve data quality and to eliminate redundant or obsolete information. Migration architecture is decided on and developed, any necessary software licenses are obtained, and change management processes are started.[1][2]
Depth Migration is applied to seismic data in depth (regular Cartesian) coordinates, which must be calculated from seismic data in time coordinates. This method does therefore require a velocity model, making it resource-intensive because building a seismic velocity model is a long and iterative process. The significant advantage to this migration method is that it can be successfully used in areas with lateral velocity variations, which tend to be the areas that are most interesting to petroleum geologists. Some of the popularly used depth migration algorithms are Kirchhoff depth migration, Reverse Time Migration (RTM), Gaussian Beam Migration and Wave-equation migration.
Migration: Hardware and software requirements are validated, and migration procedures are customized as necessary. Some sort of pre-validation testing may also occur to ensure requirements and customized settings function as expected. If all is deemed well, migration begins, including the primary acts of data extraction, where data is read from the old system, and data loading, where data is written to the new system. Additional verification steps ensure the developed migration plan was enacted in full.[1][2]
During spring and fall, Indiana bats migrate between hibernacula and summer roosting sites. In New York and Vermont, bats traveled up to 25 miles (40 km) between hibernacula and summer roosting sites in spring. This is a considerably shorter distance than what is seen in the Midwest, where bats may travel up to 300 miles (500 km). Many males remain close to hibernacula during the spring and summer rather than migrating long distances like females. Occasionally, they even roost within hibernacula during the summer. Males also roost in caves and trees during fall swarming. Few data exist for the roosting requirements of Indiana bats during spring and fall migrations; data indicate that requirements during these times are similar to summer needs in that the bats chose large trees with direct sunlight and exfoliating bark.
Data conversion Data curation Data preservation Data transformation Digital Preservation Extract, transform, load System migration
Up until the 1960s, Guatemalan migration to the US was negligible. The Department of Homeland Security's (DHS) Office of Immigration Statistics notes the first trickles of migration in the 1940s and 50s, but migration truly began to increase through the 1970s and 80s. By the 1990s, more than 100,000 migrants were coming into the US by means of green cards each decade and then that number slightly dipped in the early 2000s. More recent data is harder to gauge, as majority of Guatemalan migration is predicted to be unauthorized. The US Census data in 2000 marked 372,487 Guatemalans in the US and by 2010, the number had reached over 1 million, showing a 183% increase in Guatemalans in the US over the decade. This shows that even though "legal" migration may have slowed, migration as a whole from the country is on the rise.
There is a difference between data migration and data integration activities. Data migration is a project by means of which data will be moved or copied from one environment to another, and removed or decommissioned in the source. During the migration (which can take place over months or even years), data can flow in multiple directions, and there may be multiple migrations taking place simultaneously. The ETL (extract, transform, load) actions will be necessary, although the means of achieving these may not be those traditionally associated with the ETL acronym.
Migration refers to the movement of persons from a locality of origin to a destination place across some predefined, political boundary. Migration researchers do not designate movements 'migrations' unless they are somewhat permanent. Thus demographers do not consider tourists and travellers to be migrating. While demographers who study migration typically do so through census data on place of residence, indirect sources of data including tax forms and labour force surveys are also important.
In NUMA, each address in the global address space is typically assigned a fixed home node. When processors access some data, a copy is made in their local cache, but space remains allocated in the home node. Instead, with COMA, there is no home. An access from a remote node may cause that data to migrate. Compared to NUMA, this reduces the number of redundant copies and may allow more efficient use of the memory resources. On the other hand, it raises problems of how to find a particular data (there is no longer a home node) and what to do if a local memory fills up (migrating some data into the local memory then needs to evict some other data, which doesn't have a home to go to). Hardware memory coherence mechanisms are typically used to implement the migration.
The goal of migration is to ultimately increase spatial resolution and one of the basic assumptions made about the seismic data is that it only shows primary reflections and all noise has been removed. In order to ensure maximum resolution (and therefore maximum uplift in image quality) the data should be sufficiently pre-processed before migration. Noise that may be easy to distinguish pre-migration could be smeared across the entire aperture length during migration, reducing image sharpness and clarity.
Basically, it repositions/moves the energy (seismic data) from the recorded locations to the locations with the correct common midpoint (CMP). While the seismic data is received at the proper locations originally (according to the laws of nature), these locations do not correspond with the assumed CMP for that location. Though stacking the data without the migration corrections yields a somewhat inaccurate picture of the subsurface, migration is preferred for better most imaging recorder to drill and maintain oilfields. This process is a central step in the creation of an image of the subsurface from active source seismic data collected at the surface, seabed, boreholes, etc., and therefore is used on industrial scales by oil and gas companies and their service providers on digital computers.
Data is stored on various media in files or databases, and is generated and consumed by software applications, which in turn support business processes. The need to transfer and convert data can be driven by multiple business requirements, and the approach taken to the migration depends on those requirements. Four major migration categories are proposed on this basis.
Migration, which focuses on the digital object itself, is the act of transferring, or rewriting data from an out-of-date medium to a current medium and has for many years been considered the only viable approach to long-term preservation of digital objects.[11] Reproducing brittle newspapers onto microfilm is an example of such migration.
A variety of upgrading options are available. After migrating the data and queries to SQL Server, the Access database can be linked to the SQL database. However, certain data types are problematic, most notably "Yes/No". In Microsoft Access there are three states for the Yes/No (True/False) data type: empty, no/false (zero) and yes/true (-1). The corresponding SQL Server data type is binary, with only two states, permissible values, zero and 1. Regardless, SQL Server is still the easiest migration, and most appropriate especially if the user does not have rights to create objects such as stored procedures on SQL Server. Retrieving data from linked tables is optimized to just the records needed, but this scenario may operate less efficiently than what would otherwise be optimal for SQL Server. For example, in instances where multi-table joins still require copying the whole table across the network.
As of 2011, "nearly 40 percent of data migration projects were over time, over budget, or failed entirely."[1][3] As such, to achieve an effective data migration, proper planning is critical. While the specifics of a data migration plan may vary—sometimes significantly—from project to project, the computing company IBM suggests there are three main phases to most any data migration project: planning, migration, and post-migration.[2] Each of those phases has its own steps. During planning, dependencies and requirements are analyzed, migration scenarios get developed and tested, and a project plan that incorporates the prior information is created. During the migration phase, the plan is enacted, and during post-migration, the completeness and thoroughness of the migration is validated, documented, closed out, including any necessary decommissioning of legacy systems.[2] For applications of moderate to high complexity, these data migration phases may be repeated several times before the new system is considered to be fully validated and deployed.
Migration of seismic data is the correction of the flat-geological-layer assumption by a numerical, grid-based spatial convolution of the seismic data to account for dipping events (where geological layers are not flat). There are many approaches, such as the popular Kirchhoff migration, but it is generally accepted that processing large spatial sections (apertures) of the data at a time introduces fewer errors, and that depth migration is far superior to time migration with large dips and with complex salt bodies.
Archaeogenetics has been used to better understand the populating of the Americas from Asia. Native American mtDNA haplogroups have been estimated to be between 15 and 20 kya, although there is some variation in these estimates. Genetic data has been used to propose various theories regarding how the Americas were colonized. Although the most widely held theory suggests “three waves” of migration after the LGM through the Bering Strait, genetic data have given rise to alternative hypotheses. For example, one hypothesis proposes a migration from Siberia to South America 20-15 kya and a second migration that occurred after glacial recession. Y-chromosome data has led some to hold that there was a single migration starting from the Aldai Mountains of Siberia between 17.2- 10.1 kya, after the LGM. Analysis of both mtDNA and Y-chromosome DNA reveals evidence of “small, founding populations.” Studying haplogroups has led some scientists to conclude that a southern migration into the Americas from one small population was impossible, although separate analysis has found that such a model is feasible if such a migration happened along the coasts.
Wakame-vdc strives to provide the same experience to the entire data center, as virtual machines have done for operating systems. The VDC (Virtual Data Center) offers virtualized facilities such as servers, storage, and networking, in what can be described as a data center level hypervisor. Deployment, migration and backup of a Wakame-vdc installation can freely be replicated between any site running Wakame-vdc, with minimal reconfiguration.
DiskXtender, by intercepting I/O from operating system, is capable of detecting inactive data and then migrating those data to secondary and/or tertiary storage with lower cost/GBs while still maintaining transparency to both applications and end users. Applications and end users have full visibility of migrated data and when access is requested, those migrated data will either be redirected to users and applications or copied back to the production system.
Post-migration: After data migration, results are subjected to data verification to determine whether data was accurately translated, is complete, and supports processes in the new system. During verification, there may be a need for a parallel run of both systems to identify areas of disparity and forestall erroneous data loss. Additional documentation and reporting of the migration project is conducted, and once the migration is validated complete, legacy systems may also be decommissioned. Migration close-out meetings will officially end the migration process.[1][2]
Explained in another way, this process attempts to account for wave dispersion from dipping reflectors and also for the spatial and directional seismic wave speed (heterogeneity) variations, which cause wavefields (modelled by ray paths) to bend, wave fronts to cross (caustics), and waves to be recorded at positions different from those that would be expected under straight ray or other simplifying assumptions. Finally, this process often attempts to also preserve and extract the formation interface reflectivity information imbedded in the seismic data amplitudes, so that they can be used to reconstruct the elastic properties of the geological formations (amplitude preservation, seismic inversion). There are a variety of migration algorithms, which can be classified by their output domain into the broad categories of time migration or depth migration, and pre-stack migration or post-stack migration (orthogonal) techniques. Depth migration begins with time data converted to depth data by a spatial geological velocity profile. Post-stack migration begins with seismic data which has already been stacked, and thus already lost valuable velocity analysis information.
Most schema migration tools aim to minimize the impact of schema changes on any existing data in the database. Despite this, preservation of data in general is not guaranteed because schema changes such as the deletion of a database column can destroy data (i.e. all values stored under that column for all rows in that table are deleted). Instead, the tools help to preserve the meaning of the data or to reorganize existing data to meet new requirements. Since meaning of the data often cannot be encoded, the configuration of the tools usually needs manual intervention.
One question which was of particular interest to Rouse with regards to migrations in prehistory involves the story of the Taíno. This was the culture, which was fairly complex in social structure, that was first encountered by Old World explorers, most notably Christopher Columbus. In 1986 Rouse published "Migrations in Prehistory: Inferring Population Movement from Cultural Remains", a volume that included migratory hypotheses regarding the Taíno, along with Polynesian, Japanese and Eskimo migrations. In this volume Rouse discusses different population movements throughout the world, and discusses his view of the proper way to study prehistoric migrations. A review of this publication outlines the general technique Rouse believed would be most useful in studying migrations. The archaeologist must create testable hypotheses and inferences, with emphasis placed upon local development, acculturation, and transculturation. The hypotheses should also be tested against other forms of anthropological data, such as linguistic and physical anthropological data. In 1993 he published a book specifically about the Taíno titled "The Taíno: Rise and Decline of the People Who Greeted Columbus". The work that Rouse did on the Taíno culture is still relevant today due to what is being called the "Taíno Revival" movement, which claims that contrary to the belief of most, the Taíno people are not extinct, as most history books claim. On the contrary, the movement asserts that there are still many Taíno peoples still in existence (especially in areas like Puerto Rico) who aim to show that their culture was never destroyed, despite what history books say.
During the migration process, user data is captured from the source OS, and transferred to the Windows 7 environment. This is achieved by running the migration software on both systems and choosing their respective roles when prompted by the application. The application auto-detects migration settings. An "Advanced" option allows the user to customize the migration process, allowing sources and targets to be customized. Custom filters can limit the data transferred, e.g. skipping archives and files larger than 100MB in size.