This is what i see in the logs:
Nov 19 01:09:29 NAS2 entry.cgi_SYNO.Core.Upgrade[1].start[32691]: Upgrade.cpp:225 Verify checksum of [//upd@te]...
Nov 19 01:09:30 NAS2 entry.cgi_SYNO.Core.Upgrade[1].start[32691]: Upgrade.cpp:230 Pass checksum of //upd@te...
Nov 19 01:09:30 NAS2 entry.cgi_SYNO.Core.Upgrade[1].start[32691]: Upgrade.cpp:306 Executing [//upd@te/updater -v / -x > /dev/null 2>&1]
Nov 19 01:09:30 NAS2 updater: updater.c:5011 Start of the updater...
Nov 19 01:09:30 NAS2 updater: updater.c:5120 This is X86 platform
Nov 19 01:09:30 NAS2 updater: updater.c:5123 ==== Start flash update ====
Nov 19 01:09:30 NAS2 updater: updater.c:5135 The SynoBoot partitions exist.
Nov 19 01:09:30 NAS2 updater: updater.c:2406 orgBuildNumber = 4528, newBuildNumber=5004
Nov 19 01:09:30 NAS2 updater: updater.c:2494 [CheckPackageSize] Find [1] internal volume, external volume count= [0]
Nov 19 01:09:30 NAS2 updater: updater.c:2511 CheckPackageSize, err=0
Nov 19 01:09:30 NAS2 updater: updater.c:3176 SYNORedBootUpdCheckAndApply(3176): Skip bootloader update, no uboot_do_upd.sh exists
Nov 19 01:09:30 NAS2 updater: updater.c:354 fail to backup images. cp -f /tmp/bootmnt/rd.gz //synob@ckup
Nov 19 01:09:30 NAS2 updater: updater.c:493 checksum geneterated by [/bin/grep -i zImage checksum.syno >> /tmp/checksum.syno.tmp]
Nov 19 01:09:30 NAS2 updater: updater.c:512 file [zImage] is being copied to [/tmp/bootmnt]
Nov 19 01:09:30 NAS2 updater: updater.c:520 file [/tmp/bootmnt/zImage] process done.
Nov 19 01:09:30 NAS2 updater: updater.c:493 checksum geneterated by [/bin/grep -i rd.gz checksum.syno >> /tmp/checksum.syno.tmp]
Nov 19 01:09:30 NAS2 updater: updater.c:512 file [rd.gz] is being copied to [/tmp/bootmnt]
Nov 19 01:09:31 NAS2 updater: updater.c:520 file [/tmp/bootmnt/rd.gz] process done.
Nov 19 01:09:31 NAS2 updater: updater.c:493 checksum geneterated by [/bin/grep -i grub_cksum.syno checksum.syno >> /tmp/checksum.syno.tmp]
Nov 19 01:09:31 NAS2 updater: updater.c:512 file [grub_cksum.syno] is being copied to [/tmp/bootmnt]
Nov 19 01:09:31 NAS2 updater: updater.c:520 file [/tmp/bootmnt/grub_cksum.syno] process done.
Nov 19 01:09:31 NAS2 updater: updater.c:507 file [/tmp/bootmnt/hda1.tgz] is being removed
Nov 19 01:09:31 NAS2 updater: updater.c:520 file [/tmp/bootmnt/hda1.tgz] process done.
Nov 19 01:09:31 NAS2 updater: updater.c:507 file [/tmp/bootmnt/updater] is being removed
Nov 19 01:09:31 NAS2 updater: updater.c:520 file [/tmp/bootmnt/updater] process done.
Nov 19 01:09:31 NAS2 updater: updater.c:507 file [/tmp/bootmnt/VERSION] is being removed
Nov 19 01:09:31 NAS2 updater: updater.c:520 file [/tmp/bootmnt/VERSION] process done.
Nov 19 01:09:31 NAS2 updater: updater.c:530 checksum file updated by [/bin/cp -f /tmp/checksum.syno.tmp /tmp/bootmnt/checksum.syno]
Nov 19 01:09:39 NAS2 updater: updater.c:1136 GRUB upgrade needed file does not exist
Nov 19 01:09:39 NAS2 updater: updater.c:1516 Kernel Version: 3.2.40
Nov 19 01:09:39 NAS2 updater: updater.c:1596 failed to get old BIOS version
Nov 19 01:09:39 NAS2 updater: updater.c:5373 fail to upgrade BIOS
Nov 19 01:09:39 NAS2 updater: updater.c:610 Restoring [zImage]
Nov 19 01:09:39 NAS2 updater: updater.c:621 Copying file [//synob@ckup/zImage] as [/tmp/bootmnt/zImage], result[0]
Nov 19 01:09:39 NAS2 updater: updater.c:610 Restoring [rd.gz]
Nov 19 01:09:39 NAS2 updater: updater.c:624 Removing file [/tmp/bootmnt/rd.gz], result[0]
Nov 19 01:09:39 NAS2 updater: updater.c:607 Skip restoring [vendor]
Nov 19 01:09:39 NAS2 updater: updater.c:610 Restoring [grub_cksum.syno]
Nov 19 01:09:39 NAS2 updater: updater.c:624 Removing file [/tmp/bootmnt/grub_cksum.syno], result[0]
Nov 19 01:09:39 NAS2 updater: updater.c:610 Restoring [hda1.tgz]
Nov 19 01:09:39 NAS2 updater: updater.c:624 Removing file [/tmp/bootmnt/hda1.tgz], result[-1]
Nov 19 01:09:39 NAS2 updater: updater.c:628 Restore [hda1.tgz] fail, remove it from synoboot
Nov 19 01:09:39 NAS2 updater: updater.c:610 Restoring [updater]
Nov 19 01:09:39 NAS2 updater: updater.c:624 Removing file [/tmp/bootmnt/updater], result[-1]
Nov 19 01:09:39 NAS2 updater: updater.c:628 Restore [updater] fail, remove it from synoboot
Nov 19 01:09:39 NAS2 updater: updater.c:610 Restoring [VERSION]
Nov 19 01:09:39 NAS2 updater: updater.c:624 Removing file [/tmp/bootmnt/VERSION], result[-1]
Nov 19 01:09:39 NAS2 updater: updater.c:628 Restore [VERSION] fail, remove it from synoboot
Nov 19 01:09:39 NAS2 updater: updater.c:610 Restoring [checksum.syno]
Nov 19 01:09:39 NAS2 updater: updater.c:624 Removing file [/tmp/bootmnt/checksum.syno], result[0]
Nov 19 01:09:39 NAS2 updater: updater.c:5675 fail to rollback flash (restore)
Nov 19 01:09:39 NAS2 updater: updater.c:5711 Failed to accomplish the update! (errno = 21)
Nov 19 01:09:39 NAS2 entry.cgi_SYNO.Core.Upgrade[1].start[32691]: Upgrade.cpp:309 failed to system cmd=[//upd@te/updater -v / -x > /dev/null 2>&1], r=5376
Nov 19 01:09:39 NAS2 entry.cgi_SYNO.Core.Upgrade[1].start[32691]: Upgrade.cpp:478 Failed to unpack firmware.
Nov 19 01:09:41 NAS2 synoimgbkptool: (926) [err] network.cpp:19 lookup[]: [0x1000 net_sep_ip.c:27]
Nov 19 01:09:41 NAS2 synoimgbkptool: (932) [err] network.cpp:19 lookup[]: [0x1000 net_sep_ip.c:27]
Nov 19 01:09:42 NAS2 avahi-daemon[485]: Failed to add service 'NAS2' of type '_http._tcp', ignoring service group (/usr/syno/avahi/services/http.service): Invalid record
Nov 19 01:09:42 NAS2 avahi-daemon[1093]: Failed to add service 'NAS2' of type '_http._tcp', ignoring service group (/usr/syno/avahi/services/http.service): Invalid record
Nov 19 01:09:43 NAS2 CUPS: Starting cupsd...
Nov 19 01:09:43 NAS2 cupsd[1344]: [conf.c:1893] Filter "pstoraster" not found.
Nov 19 01:09:43 NAS2 avahi-daemon[1198]: Failed to add service 'NAS2' of type '_http._tcp', ignoring service group (/usr/syno/avahi/services/http.service): Invalid record