bootloader Archives - AWS Managed Services by Anchor

The difference between booting MBR and GPT with GRUB

By | Technical | 5 Comments

We recently talked about booting Linux from Really Big hard drives using GPT and a special boot partition. We thought we’d step back a bit and talk about why this is necessary, and how EFI bootloading differs from the classic BIOS boot. The case for GPT As we mentioned previously, you need to use GPT on disks larger than 2TB in size. The limit arises from the historical use of CHS addressing in the BIOS. In short, GPT lets you can create partitions larger than 2TB. MBR partitioning can’t do that. If you’re using a hardware RAID card you can carve out multiple less-than-2TB virtual disks and stick to MBR partitioning, and then glue them back together with LVM. It’s not ideal, but it works well. However, you’re out of…

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Booting large GPT disks without EFI

By | Technical | No Comments

In recent times we’ve been dealing with systems with more and more diskspace. Our latest deployment has a full 30TB of usable capacity! However, this presents some interesting challenges when it comes to booting the operating system. Disks larger than 2TB necessitate the use of GPT partition tables, and booting from GPT disks involves jumping through some hoops due to the way the BIOS and bootloaders work. You can dodge this bullet if you’re using a hardware RAID card, but that’s not always an option. That’s the situation we found ourselves in the other day, with some shiny new multi-terabyte drives not attached to a hardware RAID controller. We’ll gloss over a lot of the details, but the short version is that we can’t put GRUB’s stage 1.5 in the…

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