Regarding EFI system partition as the first partition on 512e based hard drive (unaligned) (performance issue?)

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I'm building my very first UEFI based server. I am manually arranging the gpt based partitions on the hard drive. I am placing the EFI system partition as the very first partition. Usually I will create a 127mb dummy partition as the very first partition to do a universal alignment (or I will create the first partition to end on sector# 262143 which will align the following partition(s) for any configuration (cluster size, raid stripes, etc)). I suppose I can be a little conservative about utilizing all possible drive space, so I was wondering: If I use this "dummy partition" as the location for the EFI system partition will it cause some kind of major performance issue? (since its a 512e drive and the partition will not be aligned) I tend to think not, since the partition is basically read one time during the boot process and not used to write files on a regular basis. But I just wanted to throw that question out there, just to be certain that I'm not doing something completely ridiculous. So is it ok to set the EFI system partition up as the first partition (unaligned) on a gpt hard drive and at the same time use it as an "offset" to align the following partitions? Thanks in advance and best regards.

Johnny The Critic

Posted 2017-07-07T23:08:04.243

Reputation: 11

Answers

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Unless you're doing sector math in an attempt to claim every single byte of possible free space on the drive, you do not need to worry about alignment. Any operating system that supports EFI is aware of 512e and 4Kn drives, and will always align partitions to 4K boundaries by default. You have to try pretty hard to mis-align them.

Really, if you're creating partitions manually, all you need to do is make sure that the starting sector of every partition is evenly divisible by 8 (512 bytes * 8 = 4096k) and you should be fine.

Also be aware that you should not allocate the last 2048 sectors on the drive to any partition. You don't mention what OS you will be running, but Windows has problems with partitions that touch the end of the drive. There are some legacy reasons for this which are too much to get into here. But it's a good idea to just leave that space alone.

Also, you should always make the EFI partition the first one on the drive. If you want, it's perfectly OK to make this partition start at sector 40. That's the first usable sector on a GPT drive. Since you're interested in nice, neat ordering, make it 262,103 sectors long. This would be 127.98MB in size. That makes your first data partition on the drive start at sector 262,144 -- exactly 128 MB from the front of the drive.

If you will be running Windows, you will also need an MSR partition. This is what Windows officially calls a "dummy" partition. It must be at least 16MB in size for Server 2016, or 64MB for Server 2012.

Wes Sayeed

Posted 2017-07-07T23:08:04.243

Reputation: 12 024

Thanks, I do always use the divide by 8 to double check that everything is aligned, its nice to hear someone confirm it. I always leave 16mb between partitions, I tell myself its in case I need to resize, etc. I also leave an odd leftover amount at the end and recently learned that is good for gpt because of the 2nd copy of the partition table isn't universally recognized and can cause issues of some kind if there is a collision. I plan to use Server 2016 (hyper-v's) and possibly if I can swing it clonezilla for creating backup images. Using the whole process to catch up on partition info. – Johnny The Critic – 2017-07-08T00:47:14.783

Oh, btw, I checked and it seems that Gparted isn't going to allow me to do the EFI partition at the first available sector (40?)... It placed the start right at 2048, I may have to boot with DOS fdisk or something to see if somehow I can do it or just leave it well enough alone. Its the first time I ever ran into an over-efficient partitioning utility situation. – Johnny The Critic – 2017-07-08T00:50:27.847

@JohnnyTheCritic; I personally use gdisk in Linux or gpt on a Mac. GParted is probably in MBR compatibility mode and that's why it won't let you go below 2048. You might be able to turn that off but I don't use GParted so I can't say. But DOS fdisk definitely won't give you the control you're seeking here. – Wes Sayeed – 2017-07-08T00:57:02.970

In terms of data structures, given a default-sized partition table and 512-byte (logical) sectors, the first usable sector on a disk is 34, not 40; but 40 is the first that's properly aligned for a disk with 4096-byte physical sectors. Most tools these days enforce 1 MiB (2048-sector) alignment by default. There are sometimes ways around this. In gdisk, you'd type x and then l (lowercase "L") to change the alignment value, then m to return to the main menu. GParted doesn't allow enough precision to do what you want, AFAIK. – Rod Smith – 2017-07-11T12:25:42.997

One more point: I recommend making the ESP 550 MiB. The reason is twofold: Some tools (like mkdosfs in Linux) will create FAT16, rather than FAT32, on partitions smaller than 500-something MiB. The cutoff value is something weird, at least for mkdosfs, so I round up. The problem with FAT16 is that some (mostly older) EFIs have flaky FAT drivers that don't handle FAT16 very well, resulting in files that seem to disappear. Likewise, some ESPs have flaky FAT drivers that don't handle FAT32 partitions smaller than 512 MiB. Thus, making the ESP 550 MiB is safe. – Rod Smith – 2017-07-11T12:29:21.563

Asked: 2017-07-07T23:08:04.243

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Active: 2017-07-07T23:50:35.147