Wrong disk capacity ( HDD on USB, OSX, EFI with 3 HFS+)

How to use TestDisk to recover lost partition
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Joined: 19 Sep 2015, 06:48

Wrong disk capacity ( HDD on USB, OSX, EFI with 3 HFS+)

#1 Post by philaga » 19 Sep 2015, 08:19


I wanted to buy you drink, but it seems that it will be little bit delayed.

I am using OSX (10.6 and 10.9), I had a 3To Barracuda on USB Dock with EFI and 3 HFS+ partitions.

While building a NAS (QNAP TS-431 with 4.1.4 ) to save all this data, I had USB bad connexions and my 3To drive (Seagate ST3000DM001-1ER166 CC26) became a 800Gb without partitions :-(

/dev/disk1 – 801 GB / 746 GiB – 1565565872 sectors

How can I correct this ? I’ve used testdisk, pdisk and gpt as describe below, and I am still in bad situation, because of this bad capacity, isn’t it ?

With testdisk : I succeed to get the normal partition information’s

———————– testdisk
Interface Advanced
hdr_lba_alt=5860533167 (expected 1565565871)
check_part_gpt failed for partition
3 P Mac HFS 1954182840 4884449423 2930266584 [sav films]
check_part_gpt failed for partition
4 P Mac HFS 4884711568 5860270983 975559416 [timemachine]
1 P EFI System 40 409639 409600 [EFI System Partition]
2 P Mac HFS 409640 1953920695 1953511056 [sav Photos]
HFS+ blocksize=4096, 1000 GB / 931 GiB
3 P Mac HFS 1954182840 4884449423 2930266584 [sav films]
4 P Mac HFS 4884711568 5860270983 975559416 [timemachine]
TestDisk exited normally.

After I’ve tryed to became a man … unfortunatly I have pratique little bit more.

With pdisk : I’ve rewrite the EFI partition, which became HFS+, I guess, and testdisk couldn’t find that the disk had a previous EFI.

With gpt : I’ve install EFI partition again, now the testdisk accept the disk as a EFI/GPT but can’t see anymore the 3 old partitions. This seems a normal effect of the rewriting EFI partition isn’t it ?

With pdisk : insert partition table information with testdisk information but :
I’ve got 2 messages : “pdisk: Can’t read block 2 from partition 2 / pdisk: Can’t read block 2 from partition 3″
and this one which underlines the bad disk capacity, isn’t it ? : “requested base and length is not within an existing free partition”
The result is a bad partition table, and a 800Gb disk to erase :-( when trying to mount it.

Partition map (with 512 byte blocks) on ‘/dev/rdisk1′
#: type name length base ( size )
1: Apple_partition_map Apple 63 @ 1
2: Apple_Free Extra 589744208 @ 64 (281.2G)
3: Apple_HFS timemachine 975559416 @ 589744272 (465.2G)
4: Apple_Free Extra 388879152 @ 1565303688 (185.4G)
5: Apple_HFS sav 2930266584 @ 1954182840 ( 1.4T)
6: Apple_Free Extra 976083744 @ 589482128 (465.4G)

Device block size=512, Number of Blocks=1565565872 (746.5G)
DeviceType=0x0, DeviceId=0x0

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