Hello 2ppisa,
should it useful mark every partition with lba flag?
This depends on the filesystem ( only DOS/Windows are concerned! ) and most of all the Partition/Volume size.
Information
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Perhaps you already know, how harddisks are constructed. They have multiple disks with magnetic layers stacked vertically, turning at high speed. Multiple heads get steered over the surfaces at very low distance, thus reading and writing data on it. From this mechanical construction derive the physical terms of storage units. The smallest unit is the (logical) "block" (512 Bytes). One track of each disk is subdivided into multiple "sectors" (of one block each). Multiple "heads" allow simultaneous access to multiple sectors of one track each, on multiple disk surfaces . The term "cylinder" means the number of concentric tracks on each disk surface. Therefore you can describe a physical disk by "cylinders","heads","sectors" (C/H/S) and calculate their total size by: cylinders x heads x sectors x 512 Bytes.
From the early days of PC up to now, the Partition Table in Master Boot Record (MBR) has limited space for this important data: Maximum C/H/S = 1023/255/63 => 8,414,461,440 Bytes => 7,84 GiB
But in addition to this physical limit exists a logical limit. Logically block units are aggregated by the (DOS) filesystem in "clusters" (a One-Byte file needs at minimum one cluster's space !). The number of clusters is limited (with older DOS/WIN versions, FAT16) to 65536, each at most 32 KB(= 64 blocks), which gives a maximum size of 2,147,483,648 Bytes (= 2 GiB).
To bypass these inherited limits, the "Logical Block Array" (LBA) concept was created. Modern harddisks exceed the above size limits by far. To mark ("flag") a filesystem as "LBA" is an important hint for the BIOS in Boot process not to use the classical C/H/S values ( which are set to 1023/255/63 as default), but to use the extended values.
Note, that C/H/S values on the harddisk label today, have nearly almost nothing to do with the actual mechanical construction of the disk. They are instead converted by its electronic to match the mechanical construction.
Can I do it without losing anything?
You do no lasting harm and most of all do not loose data. Worst case is, that your harddisk doesn't boot anymore. But fortunately you got "Gparted", and with a finger snip you are back to a running system. Extended Partitions with multiple logical volumes should be marked "LBA".
Ciao
cmdr