What is a query server in SharePoint farm?

Question

As per my understanding a farm consists of:

1. SharePoint Server
2. Database

Now the above SharePoint Server can be one of the following roles:

1. WFE
2. Application Server

So basically a SharePoint farm means:

WFE + Database Server

OR

Application Server + Database Server

But now I am also hearing the term Query Server or Index Server. What exactly are these? And does it mean that a farm can also mean the following?

1. Query Server + Database Server

2. Index Server + Database Server

Thanks

Answer 1

Query Server == Application Server.

A "query server" is an application server with only the search service (in this case the query role) role enabled.

You could also have a "Access Server" if you would only enable the Access Services role on the server because you have large loads of Access documents being processed. The query server and the search index server are usually seen separately because especially the indexing process is very taxing on the server and hence you might not want to have that on your main application server.

Answer 2

•Query server. A query server hosts query components and index partitions

Query components return search results. Each query component is part of an index partition, which is associated with a specific property database that contains metadata associated with a specific set of crawled content. You can make an index partition redundant by adding "mirror" query components to an index partition and putting them on different farm servers.

Index partitions are groups of query components, each of which holds a subset of the full text index and returns search results. Each index partition is associated with a specific property database that contains metadata that is associated with a specific set of crawled content. You can decide which servers in a farm will handle queries by creating a query component on that server. If you want to balance the load of handling queries across multiple farm servers, add query components to an index partition and associate them with the servers that you want to use to handle queries. For more information, see Add or remove a query component. You can make an index partition redundant by adding mirror query components to an index partition and putting them on different query servers.

•Crawl server. A crawl server hosts crawl components and a search administration component.

Crawl components process crawls of content sources, propagate the resulting index files to query components, and add information about the location and crawl schedule of content sources to their associated crawl databases. Crawl components are associated with a single Search service application. You can distribute the crawl load by adding crawl components to different crawl servers. You can have as many crawl components on a given crawl server as resources allow. If you have many content locations, you can add crawl components and crawl databases and dedicate them to specific content. Each crawl component on a given crawl server should be associated with a separate crawl database. For redundancy, we recommend that you have at least two crawl components. Each crawl component should be set to crawl both crawl databases. If a database grows to more than 25 million items, we recommend that you add a new crawl database and crawl component. The search administration component monitors incoming user actions and updates the search administration database. Only one search administration component is allowed per Search service application.The search administration component can run on any server, preferably either a crawl server or a query server.

http://technet.microsoft.com/en-gb/library/cc748824(v=office.14).aspx

dedicated server search

http://technet.microsoft.com/en-us/library/cc263144(v=office.12).aspx

bottom line its faster to index on another server and to query that server and giving you the power to have multiple Shared Services Provider (SSP), you can have it on the front end server but that means only one ssp. Seperating the functions into multiple servers means increase in speed and time to performe tasks. this is all under the same farm as you can see in the image above its more for mid to large scale. Rule is the more you seperate the servers functionality so they are dedicated to only that function the faster sharepoint becomes but also the cost ;)