[HTC Desire 510] huggs:
Okay so I downloaded the OTA update, rebooted to TWRP, and did a /cache partition backup.

I opened the backup file cache.ext4.win in File Viewer Lite, and got this:

/backup/ 40700 1750 1750 70 12260660577 11633 x ustar system system 56 RHT.security.selinux=u:object_r:cache_backup_file:s0
/backup/ 40700 1750 1750 0 12260660577 11501 5 ustar system system /recovery/ 40770 1750 3721 61 12444710514 11741 x ustar system cache 49 RHT.security.selinux=u:object_r:cache_file:s0
/recovery/ 40770 1750 3721 0 12444710514 11607 5 ustar system cache /recovery/log 100600 1750 1750 61 12444710514 12731 x ustar system system 49 RHT.security.selinux=u:object_r:cache_file:s0
/recovery/log 100600 1750 1750 23327 12444710514 12713 0 ustar system system __bionic_open_tzdata: couldn't find any tzdata when looking for localtime!
__bionic_open_tzdata: couldn't find any tzdata when looking for GMT!
__bionic_open_tzdata: couldn't find any tzdata when looking for posixrules!
Starting TWRP 2.8.1.0 on Fri Dec 19 02:45:28 2014
RECOVERY_SDCARD_ON_DATA := true
TW_NO_USB_STORAGE := true
I:TW_BRIGHTNESS_PATH := /sys/class/leds/lcd-backlight/brightness
I:Found brightness file at '/sys/class/leds/lcd-backlight/brightness'
I:TWFunc::Set_Brightness: Setting brightness control to 255
Starting the UI...Pixel format: 480x854 @ 32bpp
Pixel format: RGBX_8888
Not using qualcomm overlay, 'mdssfb_80000'
framebuffer: fd 4 (480 x 854)
blacklisting bma250 input device
=> Linking mtab
=> Processing recovery.fstab
I:Processing '/boot'
I:Processing '/system'
I:Processing '/cache'
I:Processing '/data'
I:Setting up '/data' as data/media emulated storage.
I:Created '/sdcard' folder.
I:mount '/data/media' '/sdcard' process ended with RC=0
I:Cannot find file /sys/class/android_usb/android0/idVendor
I:Cannot find file /sys/class/android_usb/android0/idProduct
I:mount '/data/media/0' '/sdcard' process ended with RC=0
I:Processing '/misc'
I:Processing '/external_sd'
I:Created '/external_sd' folder.
I:Processing '/usb-otg'
I:Created '/usb-otg' folder.
I:Backup folder set to '/data/media/0/TWRP/BACKUPS/FA4AFSR04556'
I:Settings storage is '/data/media/0'
Updating partition details...
I:Data backup size is 846MB, free: 249MB.
I:Cannot find file /sys/class/android_usb/android0/idVendor
I:Cannot find file /sys/class/android_usb/android0/idProduct
I:Unable to mount '/usb-otg'
I:Actual block device: '', current file system: 'vfat'
...done
I:Unmounting main partitions...

Partition Logs:
/boot | /dev/block/mmcblk0p40 | Size: 16MB
Flags: Can_Be_Backed_Up IsPresent
Primary_Block_Device: /dev/block/mmcblk0p40
Display_Name: Boot
Storage_Name: boot
Backup_Path: /boot
Backup_Name: boot
Backup_Display_Name: Boot
Storage_Path: /boot
Current_File_System: emmc
Fstab_File_System: emmc
Backup_Method: dd

/system | /dev/block/mmcblk0p43 | Size: 2012MB Used: 1336MB Free: 676MB Backup Size: 1336MB
Flags: Can_Be_Mounted Can_Be_Wiped Can_Be_Backed_Up Wipe_Available_in_GUI IsPresent
Primary_Block_Device: /dev/block/mmcblk0p43
Display_Name: System
Storage_Name: System
Backup_Path: /system
Backup_Name: system
Backup_Display_Name: System
Storage_Path: /system
Current_File_System: ext4
Fstab_File_System: ext4
Backup_Method: files

/cache | /dev/block/mmcblk0p42 | Size: 106MB Used: 5MB Free: 100MB Backup Size: 5MB
Flags: Can_Be_Mounted Can_Be_Wiped Can_Be_Backed_Up Wipe_During_Factory_Reset Wipe_Available_in_GUI IsPresent Can_Encrypt_Backup
Primary_Block_Device: /dev/block/mmcblk0p42
Display_Name: Cache
Storage_Name: Cache
Backup_Path: /cache
Backup_Name: cache
Backup_Display_Name: Cache
Storage_Path: /cache
Current_File_System: ext4
Fstab_File_System: ext4
Backup_Method: files

/data | /dev/block/mmcblk0p44 | Size: 1132MB Used: 846MB Free: 249MB Backup Size: 846MB
Flags: Can_Be_Mounted Can_Be_Wiped Can_Be_Backed_Up Wipe_During_Factory_Reset Wipe_Available_in_GUI IsPresent Has_Data_Media Can_Encrypt_Backup Is_Storage Is_Settings_Storage
Symlink_Path: /data/media/0
Symlink_Mount_Point: /sdcard
Primary_Block_Device: /dev/block/mmcblk0p44
Display_Name: Data
Storage_Name: Internal Storage
Backup_Path: /data
Backup_Name: data
Backup_Display_Name: Data
Storage_Path: /data/media/0
Current_File_System: ext4
Fstab_File_System: ext4
Backup_Method: files

/misc | /dev/block/mmcblk0p24 | Size: 1MB
Flags: IsPresent
Primary_Block_Device: /dev/block/mmcblk0p24
Display_Name: misc
Storage_Name: misc
Backup_Path: /misc
Backup_Name: misc
Backup_Display_Name: misc
Storage_Path: /misc
Current_File_System: emmc
Fstab_File_System: emmc
Backup_Method: dd

/external_sd | /dev/block/mmcblk1p1 | Size: 3773MB Used: 831MB Free: 2941MB Backup Size: 831MB
Flags: Can_Be_Mounted Can_Be_Wiped Wipe_Available_in_GUI Removable IsPresent Is_Storage
Primary_Block_Device: /dev/block/mmcblk1p1
Alternate_Block_Device: /dev/block/mmcblk1
Display_Name: Micro SDcard
Storage_Name: Micro SDcard
Backup_Path: /external_sd
Backup_Name: external_sd
Backup_Display_Name: Micro SDcard
Storage_Path: /external_sd
Current_File_System: vfat
Fstab_File_System: vfat
Backup_Method: files

/usb-otg | | Size: 0MB Used: 0MB Free: 0MB Backup Size: 0MB
Flags: Can_Be_Mounted Can_Be_Wiped Wipe_Available_in_GUI Removable Is_Storage
Primary_Block_Device: /dev/block/sda1
Alternate_Block_Device: /dev/block/sda
Display_Name: USB-OTG
Storage_Name: USB-OTG
Backup_Path: /usb-otg
Backup_Name: usb-otg
Backup_Display_Name: USB-OTG
Storage_Path: /usb-otg
Current_File_System: vfat
Fstab_File_System: vfat
Backup_Method: files

I:Loading package: TWRP (/script/ui.xml)
I:Loading package: TWRP (/data/media/0/TWRP/theme/ui.zip)
I:Loading package: TWRP (/res/ui.xml)
I:Loading resources...
I:Loading variables...
I:Loading mouse cursor...
I:Loading pages...
I:PageSet::CheckInclude loading filename: ''
I:Loading included resources...
I:Loading included variables...
I:Loading mouse cursor...
I:Loading included pages...
I:Loading page main
I:Loading page main2
I:Loading page install
I:Loading page flash_confirm
I:Loading page flash_zip
I:Loading page flash_done
I:Loading page clear_vars
I:Loading page confirm_action
I:Loading page action_page
I:Loading page singleaction_page
I:Loading page action_complete
I:Loading page filecheck
I:Loading page rebootcheck
I:Loading page wipe
I:Loading page advancedwipe
I:Loading page formatdata
I:Loading page formatdata_confirm
I:Loading page checkpartitionlist
I:Loading page partitionoptions
I:Loading page refreshfilesystem
I:Loading page selectfilesystem
I:Loading page backup
I:Loading page backupname1
I:Loading page backupname2
I:Loading page backupencryption
I:Loading page backupencryption2
I:Loading page checkbackuppassword
I:Loading page backup_run
I:Loading page restore
I:Unable to open '/data/media/0/TWRP/BACKUPS/FA4AFSR04556'
I:Loading page restore_read
I:Loading page restore_decrypt
I:Loading page try_restore_decrypt
I:Loading page restore_select
I:Loading page renamebackup
I:Loading page restore_run
I:Loading page selectstorage
I:Loading page mount
I:Loading page usb_mount
I:Loading page usb_umount
I:Loading page reboot
I:Loading page settings
I:Loading page timezone
I:Loading page screen
I:Loading page Vibrate
I:Loading page advanced
I:Loading page partsdcard
I:Loading page htcdumlock
I:Loading page lock
I:Loading page filemanagerlist
I:Loading page filemanageroptions
I:Loading page choosedestinationfolder
I:Loading page filemanagerrenamefile
I:Loading page filemanagerrenamefolder
I:Loading page filemanagerchmod
I:Loading page filemanagerconfirm
I:Loading page filemanageracction
I:Loading page decrypt
I:Loading page trydecrypt
I:Loading page terminalfolder
I:Loading page terminalcommand
I:Loading page sideload
I:Loading page installsu
I:Set page: 'clear_vars'
I:Set page: 'main2'
I:Switching packages (TWRP)
SELinux contexts loaded from /file_contexts
Full SELinux support is present.
Startup Commands:
ro.adb.qemud=1
ro.adb.secure=0
ro.com.google.clientidbase=android-google
ro.com.android.dateformat=MM-dd-yyyy
ro.com.android.dataroaming=true
ro.com.android.wifi-watchlist=GoogleGuest
ro.ril.hsxpa=1
ro.ril.gprsclass=10
ro.url.legal=http://www.google.com/intl/%s/mobile/android/basic/phone-legal.html
ro.boot.dq=PASS
ro.boot.lb=1
ro.boot.cid=SPCS_002
ro.boot.mid=0PCV10000
ro.boot.emmc=true
ro.boot.mode=recovery
ro.boot.podt=0x3E8
ro.boot.ddrmid=(0x3)
ro.boot.carrier=COMMON
ro.boot.keycaps=qwerty
ro.boot.baseband=1.46.40.0721
ro.boot.hardware=qcom
ro.boot.pagesize=2048
ro.boot.serialno=FA4AFSR04556
ro.boot.devicerev=2
ro.boot.bootloader=3.19.0.0000
ro.boot.efuse_info=SL
ro.boot.batt_poweron=good_battery
ro.emmc=0
ro.omni.device=a11
ro.omni.version=4.4.4-20141123-a11-HOMEMADE
ro.twrp.boot=1
ro.twrp.version=2.8.1.0
ro.wifi.channels=
ro.allow.mock.location=0
ro.board.platform=msm8226
ro.build.id=KTU84P
ro.build.date=Sun Nov 23 21:40:20 CET 2014
ro.build.date.utc=0
ro.build.host=bb.androidfiles.org
ro.build.tags=test-keys
ro.build.type=userdebug
ro.build.user=jmz
ro.build.display.id=omni_a11-userdebug 4.4.4 KTU84P eng.jmz.20141123.213917 test-keys
ro.build.product=a11
ro.build.version.sdk=19
ro.build.version.release=4.4.4
ro.build.version.codename=REL
ro.build.version.incremental=eng.jmz.20141123.213917
ro.build.description=omni_a11-userdebug 4.4.4 KTU84P eng.jmz.20141123.213917 test-keys
ro.build.fingerprint=htc/omni_a11/a11:4.4.4/KTU84P/eng.jmz.20141123.213917:userdebug/test-keys
ro.build.characteristics=default
ro.config.ringtone=Orion.ogg
ro.config.alarm_alert=Argon.ogg
ro.config.notification_sound=pixiedust.ogg
ro.secure=1
ro.carrier=unknown
ro.product.cpu.abi=armeabi-v7a
ro.product.cpu.abi2=armeabi
ro.product.name=omni_a11
ro.product.board=MSM8226
ro.product.brand=htc
ro.product.model=Desire 510
ro.product.device=a11
ro.product.locale.region=US
ro.product.locale.language=en
ro.product.manufacturer=htc
ro.baseband=1.46.40.0721
ro.bootmode=recovery
ro.hardware=qcom
ro.revision=0
ro.serialno=FA4AFSR04556
ro.9kramdump=0
ro.bootloader=3.19.0.0000
ro.debuggable=1
ro.modversion=OmniROM-4.4.4-20141123-a11-HOMEMADE
ro.factorytest=0
ro.setupwizard.enterprise_mode=1
net.bt.name=Android
net.change=net.bt.name
sys.usb.config=adb
init.svc.adbd=running
init.svc.healthd=running
init.svc.ueventd=running
init.svc.recovery=running
init.svc.choice_fn=stopped
twrp.crash_counter=0
dalvik.vm.lockprof.threshold=500
dalvik.vm.stack-trace-file=/data/anr/traces.txt
persist.sys.usb.config=adb
persist.sys.dalvik.vm.lib=libdvm.so
persist.sys.root_access=1
service.adb.root=1
keyguard.no_require_sim=true

/recovery/.version 100666 0 0 61 12444710514 12633 x ustar root root 49 RHT.security.selinux=u:object_r:cache_file:s0
/recovery/.version 100666 0 0 7 12444710514 12503 0 ustar root root 2.8.1.0 /recovery/recovery.fstab 100644 0 0 61 12444710514 14020 x ustar root root 49 RHT.security.selinux=u:object_r:cache_file:s0
/recovery/recovery.fstab 100644 0 0 2100 12444710514 13744 0 ustar root root # Android fstab file.
#<src> <mnt_point> <type> <mnt_flags> <fs_mgr_flags>
# The filesystem that contains the filesystem checker binary (typically /system) cannot
# specify MF_CHECK, and must come before any filesystems that do specify MF_CHECK

I can't see anything in it that really jumps out at me, so I figured I'd post it here in case someone else can get something out of it.

Best I can guess is maybe a new kernel?

If we're getting a Lollipop update, how is it to fit in our ~100MB /cache partition anyways?

If it is L, I'm gonna be mad at myself for messing around and making it impossible to update lol.