This scenario also happens on distribute setup.

1. Create a stripe volume with count 2 
2. fill up the volume with few files
3. add 2 more bricks and initiate rebalance

Bug
----
status initially shows fix-layout progress and migration. After sometime status says rebalance failed.

(attached the logs)

warning from valgrind logs

Thread 1:
==2375== Syscall param writev(vector[...]) points to uninitialised byte(s)
==2375==    at 0x3AA38CD293: writev (in /lib64/libc-2.5.so)
==2375==    by 0x62E457E: send_fuse_iov (fuse-bridge.c:59)
==2375==    by 0x62E46EC: send_fuse_data (fuse-bridge.c:95)
==2375==    by 0x62E5E6C: fuse_attr_cbk (fuse-bridge.c:402)
==2375==    by 0x62E603D: fuse_root_lookup_cbk (fuse-bridge.c:434)
==2375==    by 0xC0AC0EA: io_stats_lookup_cbk (io-stats.c:1415)
==2375==    by 0xBE843F9: sp_lookup_cbk (stat-prefetch.c:919)
==2375==    by 0xBC68548: qr_lookup_cbk (quick-read.c:440)
==2375==    by 0xBA54DF6: ioc_lookup_cbk (io-cache.c:266)
==2375==    by 0x4C29A75: default_lookup_cbk (defaults.c:46)
==2375==    by 0x4C29A75: default_lookup_cbk (defaults.c:46)
==2375==    by 0xB3FC655: dht_revalidate_cbk (dht-common.c:420)
==2375==  Address 0x7fefffa6c is on thread 1's stack
==2375==
==2375== Warning: client switching stacks?  SP change: 0xccbb0d8 --> 0x17841028
==2375==          to suppress, use: --max-stackframe=179855184 or greater
==2375== Warning: client switching stacks?  SP change: 0xccbb0d8 --> 0x17840aa0
==2375==          to suppress, use: --max-stackframe=179853768 or greater
==2375== Warning: client switching stacks?  SP change: 0x178409b8 --> 0xccbb0e0
==2375==          to suppress, use: --max-stackframe=179853528 or greater
==2375==          further instances of this message will not be shown.
==2375==

With bug 765368 getting fixed, the coredump issue seems to be fixed. Please reopen if seen again.