Yosemite Bootup Issues

using late 2012 imac running version 10.10.2, upgraded yosemite around november last year. i'm using 3 terabyte "fusion drive" 120 ssd built in. past month or so, computer has been running "slower" used to. more accurately, freeze processes, such itunes playing music or web browser, anywhere between split second , several seconds, without slowing down other more basic processes being run, such 4 corners, mouse control, , dock, , resume normal shortly after.

today, freeze started normal, never stopped. after waiting 2 minutes or so, held power button down long enough computer turn off. booted computer successfully, selected user, , typed in password. computer got stuck loading user, after waiting 2 minutes, shut computer down , tried again. ever since then, boot never gets past halfway point on loading screen before shutting down on it's own, never reaching user page.

googled problem , tried seemed obvious solution, disk utility. holding down command r while booting took me recovery drive, tried verify , repair hard drive. available drives seems following 6:
macintosh hd
macintosh hd
2 tb external raid media
iomega hdd
disk2
os x base system

each system being subprocess of odd system above it, evidenced following picture.

2 tb external raid media/iomega hdd external hard drive, contains 2 month old backup i'm hoping use worst case scenario if can't recover existing files. believe, i'm not sure, disk2 recovery drive, , not messed with, leaves 2 macintosh hds, or hd1 , hd2.
hd1 has "first aid" , "partition" tabs, while hd2 has "first aid", "erase", , "restore".
verifying hd1 revealed problem, instructing me repair it. upon finishing repair, received following error message:
"disk utility can’t repair disk. many of files possible, reformat disk, , restore backed-up files."
distraught, , after bit more googling of particular error message, found forum claimed repeating action on , on again worked. so, on 4th try of repairing hd1, repaired without error messages, bringing hope up. repairing hd1 seemed "mount" hd2 hd1, , bring correct information size of data stored on disk, total number of files, missing.

attempting verify hd2 brought following error messages, , unmounted hd2 somehow.

despite clear instructions repair disk, repair button hd2 greyed out, , mousing on reveals it's not available because "the selected disk can't written to"

tried boot in safe mode, holding down shift, didn't work. next tried entering single user mode holding down command s, did work, , using fsck -fy command, brought me following screen.



apologies low quality, can't think of better way of relaying information subpar image outside of manually transcribing long error message, if might help. main portion of error applies seems :

checking catalog file
corestoragegroup: completeiorequest - error 0xe00082ca detected lvg "macintosh hd" "many random looking numbers:
disk2: i/o error
volume macintosh hd not verified completely.

have no further ideas on try. have ideas on how fix drive before reformat , restore 2 month old backup?

 

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