Updating data and parity data with and without read caches

A method for updating data, comprising the steps of:

• receiving, with a first processing unit, a data update to a data block in a first storage device, wherein parity data for the data block is maintained in a second storage device, and wherein a parity group is comprised of the data block and the parity data,
• determining a parity group set including the parity group including the data block to update;
• determining whether a first data structure indicates that another data block in the parity group set is being updated;
• and
• sending, with the first processing unit, a message to the second processing unit including information on the parity group set including the data block to be updated and a second data structure indicating parity groups recently updated after determining that the first data structure does not indicate that another data block in the parity group set is being updated;
• sending a message, with the first processing unit, to a second processing unit controlling access to the parity group requesting control of access to the parity group after determining that the first processing unit does not control access to the parity group including the data block to update;
• determining new parity data from the data update, the data at the data block in the first storage device, and the parity data in the second storage device;
• and
• writing the data update to the data block in the first storage device and the new parity data to the second storage device.

A system for updating data, comprising

• (a) a first storage device including data at a data block;
• (b) a second storage device including parity data for the data block, wherein a parity group is comprised of the data block to be updated and the parity data;
• (c) a first processing unit;
• (d) a second processing unit;
• (e) program logic executed by the first processing unit, including:
• (i) means for receiving a data update to a data block in a first storage device, wherein parity data for the data block is maintained in a second storage device, and wherein a parity group is comprised of the data block and the parity data;
• (ii) means for sending a message to a second processing unit controlling access to the parity group requesting control of access to the parity group after determining that the first processing unit does not control access to the parity group including the data block to update;
• (iii) means for determining new parity data from the data update, the data at the data block in the first storage device, and the parity data in the second storage device;
• (iv) means for writing the data update to the data block in the first storage device and the new parity data to the second storage device;
• (v) means for determining a parity group set including the parity group including the data block to update after receiving the data update;
• (vi) means for processing a first data structure to determine whether another data block in the parity group set is being updated;
• and
• (vii) means for sending a message to the second processing unit including information on the parity group set including the data block to be updated and a second data structure indicating parity groups recently updated after determining that the first data structure does not indicate that another data block in the parity group set is being updated.

An article of manufacture for use in programming a first processing unit to update data at a data block in a first storage device with a data update, wherein parity data for the data block is maintained in a second storage device, wherein a parity group is comprised of the data block to be updated and the parity data, the article of manufacture comprising at least one computer readable storage device including at least one computer program embedded therein that causes the first processing unit to perform the steps of:

• receiving a data update to a data block in a first storage device, wherein parity data for the data block is maintained in a second storage device, and wherein a parity group is comprised of the data block and the parity data;
• processing by the first processing unit a first data structure indicating parity groups controlled by a second processing unit and determining, from processing the first data structure, that the second processing unit controls access to the parity group;
• sending a message to the second processing unit controlling access to the parity group requesting control of access to the parity group after determining that the first processing unit does not control access to the parity group including the data block to update;
• modifying the first data structure by the first processing unit to indicate that the first processing unit controls access to the parity group after receiving a message from the second processing unit granting control of access to the parity group, wherein the article of manufacture further comprises at least one computer program that causes the second processing unit to perform the steps of modifying a second data structure to indicate that that first processing unit controls access to the parity group to which the second processing unit granted control;
• determining new parity data from the data update, the data at the data block in the first storage device, and the parity data in the second storage device;
• and
• writing the data update to the data block in the first storage device and the new parity data to the second storage device.

An article of manufacture for use in programming a first processing unit to update data at a data block in a first storage device with a data update, wherein parity data for the data block is maintained in a second storage device, wherein a parity group is comprised of the data block to be updated and the parity data, the article of manufacture comprising at least one computer readable storage device including at least one computer program embedded therein that causes the first processing unit to perform the steps of:

• receiving a data update to a data block in a first storage device, wherein parity data for the data block is maintained in a second storage device, and wherein a parity group is comprised of the data block and the parity data,
• determining, by the first processing unit, a parity group set including the parity group including the data block to update;
• determining, by the first processing unit, whether a first data structure indicates that another data block in the parity group set is being updated;
• and
• sending a message from the first processing unit to a second processing unit including information on the parity group set including the data block to be updated and a second data structure indicating parity groups recently updated after determining that the first data structure does not indicate that another data block in the parity group set is being updated;
• sending a message to the second processing unit controlling access to the parity group requesting control of access to the parity group after determining that the first processing unit does not control access to the parity group including the data block to update;
• determining new parity data from the data update, the data at the data block in the first storage device, and the parity data in the second storage device;
• and
• writing the data update to the data block in the first storage device and the new parity data to the second storage device.

A memory for storing data for access by a first processing unit comprising ownership data indicating parity groups controlled by the first processing unit and a second processing unit, wherein a parity group is comprised of a data block and parity data for the data block, wherein the first processing unit processes the ownership data to determine whether the first processing unit controls access to the parity group after receiving update data to a data block in the parity group, wherein the first processing unit sends a message to the second processing unit controlling access to the parity group requesting control of access to the parity group after determining that the first processing unit does not control access thereto, wherein the first processing unit determines the new parity data from the data update, the data at the data block, and the parity data and writes the data update to the data block in the first storage device and the new parity data to the second storage device;

• wherein the ownership data processed by the first processing unit is first ownership data, wherein the first processing unit modifies the first ownership data to indicate that the first processing unit controls access to the parity group after receiving a message from the second processing unit granting control of access to the parity group, further comprising a second memory including second ownership data for access by the second processing unit indicating parity groups controlled by the second processing unit and the first processing unit, wherein the second processing unit modifies the second ownership data to indicate that that first processing unit controls access to the parity group to which the second processing unit granted control.