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catkin 05-09-2011 08:10 AM

Advisability of using a legacy MBR when the installer chooses GPT?
 
Hello :-)

We installed Debain 6.0 (Squeeze) on a Seagate ST2000DL003 (2 TB SATA HDD) and the installer choose GPT for us. Only came to light when we tried to run fdisk and got "WARNING: GPT (GUID Partition Table) detected on '/dev/sda'! The util fdisk doesn't support GPT. Use GNU Parted". parted was not installed by default (!). Investigating further we found dd cannot be used to back up and restore GPT; for that you need gptfdisk (a.k.a. gdisk) which is still in beta and does not have a 64-bit .deb.

Clearly GPT is the future but I am not convinced it is mature yet (Bug#599437) and the online knowledgebase is not yet extensive.

Taking all this into account, I am considering changing to a traditional MBR and included partition table. [Note on terminology: when using a GPT, the MBR is considered distinct from the partition table; when using a legacy partition table, the partition table is commonly considered part of the MBR]

Would this be wise? If the good people at Debian have programmed the installer to use GPT for this HDD, despite GPT's youth, they must have had their reasons. The most informative Debian documentation found is the Debian GNU/Linux Installation Guide, 6.3.3. Partitioning and Mount Point Selection which says "... Defaults may vary as well. The type of partition table used by default can for example be different for large capacity hard disks than for smaller hard disks. Some options can only be changed when installing at medium or low debconf priority; at higher priorities sensible defaults will be used".

Best

Charles

business_kid 05-10-2011 03:12 AM

My first reaction is this: Always, in my memory since about 1990, there has been limits on disk size. It was 528megs, 2 gigs, then higher as people tweaked the formations, and has continued to rise. Debian imho is usually the last to hop on board new technology, so you (Or some boxes) may well have trouble with a mbr on a 2TB disk. Bios versions often matter here.

gpt needs gpt tools: that's ok. Don't run scared of beta. Back around kernel 2.4.18, a sysadmin found herself with no sata support and ended up with an _alpha_ 2.6 kernel online to get her chipset. It was hard work to get it going, but it ran without incident, and she updated it in time.

catkin 05-11-2011 02:38 AM

Thanks business_kid :)

At 2 TB, the Seagate ST2000DL003 is within legacy MBR's capability but it is a 4 kB sector model so probably performs better with GPT.

Looks like I've just booked a trip to the future. Fasten seatbelts -- we could be in for a bumpy ride ... :hattip:

cascade9 05-11-2011 02:47 AM

Quote:

Originally Posted by catkin (Post 4352869)
At 2 TB, the Seagate ST2000DL003 is within legacy MBR's capability but it is a 4 kB sector model so probably performs better with GPT.

GPT/MBR shouldnt make any real performance difference. Provided that with 4k sector drives the sectors are aligned anyway.

I have used a 4k WD drive with MBR, and while it wasnt fun setting it up the drive runs just fine (and gets the speeds it should get as well). I really dont know that much about how seagate is doing 4k sectors, I dont buy seagate drives anymore, so I'm no help on alignment. Sorry.


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