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#1 2014-11-04 18:08:41

eriks
Member
Registered: 2013-06-11
Posts: 37

Really still need EBS (Erase Block Size) for partitioning a SSD?

The Arch wiki mentions that when partitioning an SSD you need to align the partitions to the erase block size (see https://wiki.archlinux.org/index.php/Pa … ate_drives ). There are a lot of how-to-partition-an-ssd-under-linux which also mention this value, even an online calculater.

Those value are known for a lot of the serious models, among them also the Samsung 840 Pro and EVO. As I already asked in an older thread, I would like to know the value for the current model Samsung 850 Pro. Unfortunately Samsung Germany's support refuses to provide me with those values.

Therefore I ask myself, is it still necessary to align partititions to a multiple of the EBS, or is this unnecessary if the device supports TRIM?

Thanks!

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#2 2014-11-04 18:55:09

2ManyDogs
Forum Fellow
Registered: 2012-01-15
Posts: 4,645

Re: Really still need EBS (Erase Block Size) for partitioning a SSD?

Did you read the section immediately after the one you linked? https://wiki.archlinux.org/index.php/Pa … ng_tools_2

In past, proper alignment required manual calculation and intervention when partitioning. Many of the common partition tools now handle partition alignment automatically:
...
To verify a partition is aligned, query it using /usr/bin/blockdev as shown below, if a '0' is returned, the partition is aligned

Is that not sufficient for your purposes?

Last edited by 2ManyDogs (2014-11-04 18:55:37)

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#3 2014-11-05 08:47:50

eriks
Member
Registered: 2013-06-11
Posts: 37

Re: Really still need EBS (Erase Block Size) for partitioning a SSD?

I'm not sure about the following paragraph in the wiki. Obviously different SSD models have very different EBS value (840 Evo vs. 840 Pro = 1024 KiB vs. 1536 KiB) those tools would need to know the value for a specific model, too. I doubt that the values for the 850 Pro are compiled in one of the partition tools. Gdisk defaults to

> On new disks, GPT fdisk attempts to align partitions on  2048-sector  (1MiB) 
> boundaries  by  default, which  optimizes  performance  for all of these disk types.

The 840 EVO e.g. has an EBS of 1536 KiB, the 840 Pro on of 1024 KiB.

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#4 2014-11-05 13:59:56

frostschutz
Member
Registered: 2013-11-15
Posts: 1,425

Re: Really still need EBS (Erase Block Size) for partitioning a SSD?

Reads/writes are aligned on page size, and erases happen in the background when the SSD is idle. As such, erase block size does not matter. Page size matters, but it's always small so just do MiB-alignment. The filesystem will break it down to something around 4k anyway. It's not possible to align to 1536KiB, not with hundreds of small files in a filesystem. Even if you were to put your partitions on 1536KiB boundaries and set your filesystem up with a 1536KiB raid stride, you would not notice any difference. Reads/writes are done on page level, and redistributed anyway by a flash translation layer. So no matter how much you try to align from the outside, the SSD will mangle it to its own purposes anyway, so what's the point?

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#5 2014-11-05 14:42:16

eriks
Member
Registered: 2013-06-11
Posts: 37

Re: Really still need EBS (Erase Block Size) for partitioning a SSD?

Frostschutz, thanks for the clarification, this make things a lot easier of course. I'll update the wiki page accordingly.

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