exemplary embodiments are directed to optimizing performance of read functions in a memory system that includes a memory controller , a primary memory , and a back - up memory that mirrors the primary memory in terms of the stored data . the primary memory and the back - up memory may include volatile memory devices ( e . g ., dram ) and / or non - volatile memory devices ( e . g ., flash ). non - volatile memory can degrade over time , under thermal loads , or due to other effects such that one or more memory failure events can occur . based on the extent of the failure , an entire chip may be marked as faulty or a portion of the chip may be marked as such . for example , when a few bits associated with a chip are determined to be faulty , a symbol mark may be used to designate the nature of the fault likewise , if a significant portion of the chip is determined to be faulty , then a chip mark may be used to designate the nature of the fault . in exemplary embodiments , memory failure events are discovered and corresponding failure event information is tracked by the memory system . a memory failure event refers to one or more bit errors detected by an error correction code decoder . these errors may have occurred due to data corruption detected at a channel level or corruption in the memory array itself . when a read request is received at the memory system , the failure event information is searched to determine if a physical location corresponding to a logical address provided in the read command is compromised . if so , the memory system is configured to direct the read request to one of the primary memory and the back - up memory based on the failure event information . the failure event information may include physical addresses of memory devices affected by the failure event , an identifier of the primary or back - up memories in which the failure event occurred , a failure event type ( e . g ., whether the failure event involves an entire chip or a portion thereof ), and other desired information , as will be described further herein . fig1 illustrates a block diagram of a system 100 operable to optimize the performance of read functions in a memory system in accordance with an embodiment . the system 100 depicted in fig1 includes a computer processor 102 , memories 106 a and 106 b ( each of which includes multiple memory devices ), and a memory controller 104 . examples of non - volatile memory devices that can incorporate embodiments as described herein include phase - change memory ( pcm ), magnetoresistive random - access memory ( mram ), ferroelectric ram ( feram ), nonvolatile static ram ( nvsram ), and restrictive ram ( reram ), as well as other non - volatile memory technologies known in the art . the memories 106 a and 106 b respectively represent a primary memory and a back - up memory ( also referred to as a mirrored memory ). the memory controller 104 reads data from the memories 106 a and 106 b in response to a read request , and may also write data to the memories 106 a and 106 b in response to a write request . collectively , the memory controller 104 and the memories 106 a and 106 b are referred to herein as a memory system 105 . in one embodiment , the memory controller 104 is coupled to the computer processor 102 and receives read requests from the computer processor 102 . the read requests contain a logical address for the data to be read from memory . this data to be read from memory is also referred to herein as “ target data .” the memory controller 104 stores data at a physical address within the primary memory ( e . g ., 106 a ) and the back - up memory ( e . g ., 106 b ). in an embodiment , the memory controller 104 maps the logical address to a physical address in the memories 106 a and 106 b when storing or retrieving data . the system 100 is one example of a configuration that may be utilized to perform the processing described herein . although the system 100 has been depicted with only the memories 106 a / 106 b , the memory controller 104 , and the computer processor 102 , it will be understood that other embodiments would also operate in other systems including additional elements , e . g ., multiple computer processors 102 and multiple levels of memory . in an embodiment , the memories 106 a and 106 b , memory controller 104 , and computer processor 102 are not located within the same computer . for example , the memories 106 a and 106 b and memory controller 104 may be located in one physical location while the computer processor 102 is located in another physical location ( e . g ., the computer processor 102 accesses the memory controller 104 via a network ). in addition , portions of the processing described herein may span one or more of the memories 106 a and 106 b , memory controller 104 , and computer processor 102 . fig2 illustrates a block diagram of a memory system 200 operable to optimize the performance of read functions in accordance with an embodiment . the memory system 200 is an embodiment of the memory system 105 of fig1 . in the example of fig2 , memory controller 202 is operably coupled to a primary memory 210 a and its memory devices 1 - n ( collectively , 204 a ) and also to a back - up memory 210 b and its memory devices 1 - n ( collectively , 204 b ). the back - up memory 210 b is redundant storage and mirrors the data stored in the primary memory 210 a . command , address , and data buses ( collectively “ 206 ”) enable read and write requests to be issued from the memory controller 202 to the memory devices 204 a and 204 b . the busses 206 may be implemented as direct memory interface ( dmi ) channels . a read request 208 may be driven as a discrete signal output from a computer processor to the memory controller 202 . each of the primary memory 210 a and the back - up memory 210 b may store an error correction code ( ecc ) unit , respectively 212 a and 212 b . the ecc units 212 a and 212 b may further include error correcting logic that performs error detection and corrections for memory failure events . in an embodiment , the memory controller 202 stores a fault management table ( fmt ) 214 for tracking memory failure events identified by the ecc units 212 a and 212 b , e . g ., symbol marks and / or chip marks in a memory array or buffer . each of the memory devices 204 a and 204 b can assert an indicator based on detecting at least one memory failure event ( e . g ., chip mark or symbol mark ) found in a corresponding memory device . for example , if a memory failure event is detected by ecc unit 212 b , the error is reported to the memory controller 202 over the bus 206 , along with failure event information and a corresponding physical address of the memory failure event . the fmt 214 stores the physical address of the memory failure event in an entry of the fmt , along with an identifier of the memory ( e . g ., 210 a or 210 b ). additional details of the fmt 214 are described further in fig3 . the detected memory failure events are transmitted over busses 206 to the memory controller 202 , as will be described further herein . while only a single ecc unit 212 a and 212 b is shown in each of the memories 210 a and 210 b , it will be understood that other configurations are possible . for example , a separate ecc unit may be stored in the corresponding memories for each of the memory devices . as shown in fig3 , a fmt 300 , which corresponds to fmt 214 of fig2 , includes a number of entries , each of which corresponds to a memory failure event identified , e . g ., by the ecc units 212 a and 212 b . a first column 302 specifies a physical address of a memory device corresponding to the memory failure event . a second column 304 specifies in which of the primary memory 210 a ( labeled “ p ”) and the back - up memory 210 b ( labeled “ b ”) the memory failure event occurred . a third column 306 specifies the type of memory failure event ( e . g ., chip mark or symbol mark ). a fourth column 308 specifies bit errors ( b / e ) detected ( labeled “ m1 - mn ”), whereby m1 through mn indicate bit errors , m1 & lt ; m2 . . . & lt ; mn . the ecc decoders for the primary and secondary memories have the same level of error correction capabilities . if both primary and secondary memories do not have similar fault conditions , then the controller would choose the memory with the minimum fault ( e . g ., the memory having fewer bit errors ). if both the primary memory and the secondary memory have the same fault conditions , then either the primary or secondary memory may be selected . a fifth column 310 tracks the number of occurrences of the memory failure event identified for a particular memory device , which memory device can be ascertained based on the physical address . the number of occurrences can be tracked over a specified period of time . fig4 illustrates a flow diagram of a method 400 for optimizing the performance of read functions in accordance with an embodiment . the depicted blocks may be part of or in addition to another process and / or may be performed in any suitable order to provide optimized performance of read functions . the method 400 can be implemented for a variety of memory system configurations and is described in reference to fig1 - 3 . for instance , the method 400 can be performed by the memory controller 202 , one or both of memories 210 a and 210 b , or by one or more non - volatile memory devices 204 a and 204 b . at block 402 , the memory system 200 receives a read request including a logical address of a target data . the read request is received from a computer processor ( e . g ., computer processor 102 of fig1 ). at block 404 , the memory system 200 ( e . g ., via the memory controller 202 ) searches the fmt 214 for an entry corresponding to the received logical address . each of the entries in the fmt 214 indicates a physical location of identified memory failure events in the primary memory 210 a and the back - up memory 210 b . at block 406 , the memory system 200 determines whether an entry corresponding to the received logical address is found in the fmt 214 . if not , this means that no memory failure events were detected at the physical address of the target data in either the primary memory 210 a or the back - up memory 210 b . in this instance , the read request is directed to the primary memory 210 a for retrieving the target data at block 408 . alternatively , the read request may be directed to one of the memories 210 a or 210 b based on a default function . however , if no entry corresponding to the received logical address is found in the fmt 214 at block 406 , this means that a memory failure event has been identified for the respective physical address of the target data . in this instance , the memory system 200 handles the read request based on the contents of the fmt table 214 . in an embodiment , criteria may be established for determining which of the primary memory 210 a and the back - up memory 210 b to use for directing read requests . the criteria may be based on the type or severity of memory failure event identified ( chip mark or symbol mark ), or may be based on a frequency of errors detected for a particular memory device associated with the target data . the fmt 214 stores the memory failure event information ( e . g ., type of failure event , frequency of detection of the failure event , etc .). thus , at block 410 , the memory system 200 determines which of the primary memory 210 a and the back - up memory 210 b the read request will be directed . in an embodiment , the memory system 200 is configured to receive the memory failure event information when it occurs or has been discovered , and store the memory failure event information in the fmt 214 . for example , the memory system 200 receives an indication from one of the primary memory 210 a and the back - up memory 210 b of a symbol mark or chip mark for a memory device ( one of memory devices 1 - n in fig2 ). the memory system 200 enters the memory event failure information in an entry of the fmt 214 . the memory failure information includes the physical location ( e . g ., physical address of the memory device and an identifier of which of the primary memory 210 a or back - up memory 210 b the memory failure event is located ) in columns 302 and 304 . the memory failure event information may also include the type of error ( e . g ., symbol mark or chip mark ) and bit errors in columns 306 and 308 , and / or other useful information , such as the frequency of occurrence of the error for a particular memory device in column 310 . likewise , when the memory system 200 receives a correction notice or indicator that one of the symbol marks or chip marks has been resolved ( e . g ., from the ecc unit ), the memory system 200 updates the fmt 214 to remove the corresponding entry . technical effects include performance optimization of read functions in a memory system by tracking memory failure event information including corresponding primary and back - up memories in which the memory failure event occurred , and retrieving requested data from the unaffected memory , thereby minimizing the latency otherwise incurred when request for data is first issued to a memory affected by a memory failure event . the present invention may be a system , a method , and / or a computer program product . the computer program product may include a computer readable storage medium ( or media ) having computer readable program instructions thereon for causing a processor to carry out aspects of the present invention . the computer readable storage medium can be a tangible device that can retain and store instructions for use by an instruction execution device . the computer readable storage medium may be , for example , but is not limited to , an electronic storage device , a magnetic storage device , an optical storage device , an electromagnetic storage device , a semiconductor storage device , or any suitable combination of the foregoing . a non - exhaustive list of more specific examples of the computer readable storage medium includes the following : a portable computer diskette , a hard disk , a random access memory ( ram ), a read - only memory ( rom ), an erasable programmable read - only memory ( eprom or flash memory ), a static random access memory ( sram ), a portable compact disc read - only memory ( cd - rom ), a digital versatile disk ( dvd ), a memory stick , a floppy disk , a mechanically encoded device such as punch - cards or raised structures in a groove having instructions recorded thereon , and any suitable combination of the foregoing . a computer readable storage medium , as used herein , is not to be construed as being transitory signals per se , such as radio waves or other freely propagating electromagnetic waves , electromagnetic waves propagating through a waveguide or other transmission media ( e . g ., light pulses passing through a fiber - optic cable ), or electrical signals transmitted through a wire . computer readable program instructions described herein can be downloaded to respective computing / processing devices from a computer readable storage medium or to an external computer or external storage device via a network , for example , the internet , a local area network , a wide area network and / or a wireless network . the network may comprise copper transmission cables , optical transmission fibers , wireless transmission , routers , firewalls , switches , gateway computers and / or edge servers . a network adapter card or network interface in each computing / processing device receives computer readable program instructions from the network and forwards the computer readable program instructions for storage in a computer readable storage medium within the respective computing / processing device . computer readable program instructions for carrying out operations of the present invention may be assembler instructions , instruction - set - architecture ( isa ) instructions , machine instructions , machine dependent instructions , microcode , firmware instructions , state - setting data , or either source code or object code written in any combination of one or more programming languages , including an object oriented programming language such as smalltalk , c ++ or the like , and conventional procedural programming languages , such as the “ c ” programming language or similar programming languages . the computer readable program instructions may execute entirely on the user &# 39 ; s computer , partly on the user &# 39 ; s computer , as a stand - alone software package , partly on the user &# 39 ; s computer and partly on a remote computer or entirely on the remote computer or server . in the latter scenario , the remote computer may be connected to the user &# 39 ; s computer through any type of network , including a local area network ( lan ) or a wide area network ( wan ), or the connection may be made to an external computer ( for example , through the internet using an internet service provider ). in some embodiments , electronic circuitry including , for example , programmable logic circuitry , field - programmable gate arrays ( fpga ), or programmable logic arrays ( pla ) may execute the computer readable program instructions by utilizing state information of the computer readable program instructions to personalize the electronic circuitry , in order to perform aspects of the present invention . aspects of the present invention are described herein with reference to flowchart illustrations and / or block diagrams of methods , apparatus ( systems ), and computer program products according to embodiments of the invention . it will be understood that each block of the flowchart illustrations and / or block diagrams , and combinations of blocks in the flowchart illustrations and / or block diagrams , can be implemented by computer readable program instructions . these computer readable program instructions may be provided to a processor of a general purpose computer , special purpose computer , or other programmable data processing apparatus to produce a machine , such that the instructions , which execute via the processor of the computer or other programmable data processing apparatus , create means for implementing the functions / acts specified in the flowchart and / or block diagram block or blocks . these computer readable program instructions may also be stored in a computer readable storage medium that can direct a computer , a programmable data processing apparatus , and / or other devices to function in a particular manner , such that the computer readable storage medium having instructions stored therein comprises an article of manufacture including instructions which implement aspects of the function / act specified in the flowchart and / or block diagram block or blocks . the computer readable program instructions may also be loaded onto a computer , other programmable data processing apparatus , or other device to cause a series of operational steps to be performed on the computer , other programmable apparatus or other device to produce a computer implemented process , such that the instructions which execute on the computer , other programmable apparatus , or other device implement the functions / acts specified in the flowchart and / or block diagram block or blocks . the flowchart and block diagrams in the figures illustrate the architecture , functionality , and operation of possible implementations of systems , methods , and computer program products according to various embodiments of the present invention . in this regard , each block in the flowchart or block diagrams may represent a module , segment , or portion of instructions , which comprises one or more executable instructions for implementing the specified logical function ( s ). in some alternative implementations , the functions noted in the block may occur out of the order noted in the figures . for example , two blocks shown in succession may , in fact , be executed substantially concurrently , or the blocks may sometimes be executed in the reverse order , depending upon the functionality involved . it will also be noted that each block of the block diagrams and / or flowchart illustration , and combinations of blocks in the block diagrams and / or flowchart illustration , can be implemented by special purpose hardware - based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions . the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention . as used herein , the singular forms “ a ”, “ an ” and “ the ” are intended to include the plural forms as well , unless the context clearly indicates otherwise . it will be further understood that the terms “ comprises ” and / or “ comprising ,” when used in this specification , specify the presence of stated features , integers , steps , operations , elements , and / or components , but do not preclude the presence or addition of one more other features , integers , steps , operations , element components , and / or groups thereof . the corresponding structures , materials , acts , and equivalents of all means or step plus function elements in the claims below are intended to include any structure , material , or act for performing the function in combination with other claimed elements as specifically claimed . the description of the present invention has been presented for purposes of illustration and description , but is not intended to be exhaustive or limited to the invention in the form disclosed . many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention . the embodiment was chosen and described in order to best explain the principles of the invention and the practical application , and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated .