When comparing xBOD values, one needs to consider several factors. In addition to the manufacturer’s recommendation, one must check the speed of the source port to ensure that the source can meet its own needs. These factors are outlined in the table below. If you are not sure what these numbers mean, you can learn about their importance and how to calculate them. Read on to discover how to calculate xBOD value. We also have some tips on calculating xBOD value.
The first of two situations in which BODs and HBAs differ is when high-speed source devices request to read data from a low-speed source device. Such a request causes a blocking condition in the source port receive buffers. This situation is called BOD 254, and the invention describes an embodiment for both cases. This article will discuss the first scenario and describe embodiments for the second situation.
An xBOD is a group of disk drives connected in a single logical unit. This type of storage device is also known as a SCSI array. The data that is collected by the drive is sent through the logical unit to the destination device. It is possible to connect up to six BODs in a single array. Each xBOD consists of at least three disks. The logical unit is connected to another via a port. The ports are connected to one another through a trunking mechanism.
In order to issue write requests to the xBOD, a HBA must be connected to the same source port. If more than one xBOD is attached to a single switch, the data written to the first one may be backed up in the source port receive buffer 150. If this backup is present, data cannot be written to the xBOD. This logical arrangement prevents data from being written to an xBOD.
The blocking condition of xBOD 254 may also occur when a high-speed source device is attempting to write data to a low-speed destination device. In this case, data is not transferred from the high-speed source device to the low-speed destination device. The high-speed source device requests to write data to the low-speed destination device, and this action creates a blocking condition in the destination port’s receive buffers. The embodiments of the present invention address this problem and provide a method and system for handling it.
HBA 104 issues read and write requests to multiple xBODs, and these requests may be blocked if both xBODs are attached to the same source port. This is also true for write requests, which are issued from an HBA to a different port on a switch. However, the xBOD 108 may be slower than the HBA 104, and data that is written to it may be backed up in the source port receive buffer 150. This causes HBA 104 to fail to write data to it.
xBODs and HBAs operate at their maximum line rate and signaling rate, respectively. The difference is in the signaling rates of the source and destination devices. In the case of an xBOD, the higher line rate device is called the high speed source device, and the lower line rate device is known as the low-speed destination. However, this is not always the case. In some instances, it is possible to use an xBOD without any external device, such as a hard drive.
Another example of a blocking situation is a source device that requests to write data to a high-speed destination device. The high-speed source device has xBOD 254, but is in the xBOD 108. This results in a blocking condition in the source port receive buffers, whereas data from the low-speed destination device may be stored in an empty transmit buffer. In such a case, the xBOD 108 and xBOD 210 are both applicable to the second situation.
xBOD 254 sends R_RDY primitive
The HBA 206 sends an OPN primitive request to the switches 202 and 252. When this request is received, the drive in xBOD 254 collects the data requested and transmits an R_RDY primitive back to the source port. The R_RDY primitive opens the connection. Once the connection is established, all subsequent requests will be routed separately over either a high-speed or a low-speed trunk, with no impediment to the flow of data.
This process is repeated until the destination port receives data from the source device. If this happens too quickly, the destination device will experience a blocking condition, and data will be lost. In the following example, the high-speed source device will request to write data to the destination device. The second situation will result in a blocking condition in the source port receive buffers. Therefore, the embodiments of the present invention will be applicable to both scenarios.
xBODs attached to the same source port share receive buffers. This blocking condition can occur when multiple HBAs issue separate write requests to the same BOD. The data being written to the xBOD may be backed up in the source port receive buffer 150, thus preventing the HBA from writing the data to the BOD. This prevents the HBA from writing data to the xBOD 110.