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Maddah, Rakan (2015) A DATA AWARE APPROACH TO SALVAGE THE ENDURANCE OF PHASE-CHANGE MEMORY. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Phase Change Memory (PCM) is an emerging non-volatile memory technology that could either replace or augment DRAM and NAND flash that are hindered by scalability challenges. PCM suffers from a limited endurance problem that needs to be alleviated before it can be endorsed
into the memory stack. This thesis is based on the observation that the endurance problem and its ramification depend on the write data. Accordingly, a data-aware approach is applied to salvage the endurance of PCM at three different stages: pre-write fault avoidance, post-write fault tolerance and post-failure recovery.

The pre-write fault avoidance stage aims at reducing the endurance cost of servicing write requests. To this end, Cost Aware Flip Optimization (CAFO) is presented as an efficient technique to lessen the endurance degradation. Essentially, CAFO relies on a cost model that captures the endurance cost of programming memory cells based on their already stored values. Subsequently,the write data is encoded into a form that incurs a lower endurance cost than the original write data. Overall, CAFO is capable of reducing the endurance cost by up to 65% more than the existing schemes.

Worn out PCM cells exhibit a stuck-at fault model which makes the manifestation of errors dependent on the values that cells are stuck at. When a write fails, the data is rewritten inverted. This dissertation shows that applying data inversion at the post-write fault tolerance stage exploits the data dependent nature of errors which enables ECCs to tolerate faults up to double their nominal capability. Furthermore, extensions to RDIS which is an ECC designed specifically for the stuck-at fault model are presented.

At the post-failure recovery stage, Data Dependent Sparing is presented to manage bad blocks in PCM. Departing from the observation that defective blocks in the context of the stuck-at fault model still exhibit a low write failure probability due to the data dependent nature of errors, this thesis takes the approach of reusing blocks that are defective yet better-than-bad through a dynamic management of the reserve spare space. Data Dependent Sparing is capable of increasing the
lifetime of PCM by up to 18%.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairMelhem, Ramimelhem@cs.pitt.eduMELHEM
Committee MemberCho,
Committee MemberZnati, Taiebznati@cs.pitt.eduZNATI
Committee MemberZhang, Youtaozhangyt@cs.pitt.eduYOUTAO
Committee MemberChen, Yiranyic52@pitt.eduYIC52
Date: 27 September 2015
Date Type: Publication
Defense Date: 4 May 2015
Approval Date: 27 September 2015
Submission Date: 15 May 2015
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 125
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Computer Science
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: PCM, Endurance, Bit Flip Reduction, ECC, Bad Block Management
Date Deposited: 27 Sep 2015 22:02
Last Modified: 15 Nov 2016 14:28


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