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Large disk totally low write speed (in ~8 times lower) - Possible alignment problem.

Topics: Technical Issues
Feb 20, 2015 at 10:28 PM
Edited Feb 20, 2015 at 10:30 PM
Did You try to work with disk with 4k sectors, like ST6000NM0024? It's very fast 6 Tb disk.
If We create encrypted container in file on usual existing (NTFS) partition- all work fast ~150-200 Mb/Sec
But if We encrypt total drive (Encrypt non-system drive, Standard VeraCrypt Volume)
Write speed 10-24 Mb/Sec. 24 at begin of disk and slower to end of disk.
It's problem remains from TC - it's same problem.
(Reading is ok - fast ~180-200 Mb/Sec)
I think 4k sector writes as 512 sector * 8 - 8 times and therefore 8 times slower. Some alignment problem.

Can You find out and refine?

Thank You very much for continue working with TC idea.
Feb 21, 2015 at 12:18 AM
Have you contacted Seagate support for this Enterprise class drive for their assistance?

http://knowledge.seagate.com/articles/en_US/FAQ/221411en?language=en_US

http://www.seagate.com/tech-insights/advanced-format-4k-sector-hard-drives-master-ti/
The process of reading the 4K block of data and reformatting the specific 512- byte virtual sector requested by the host computer is performed in the drive’s DRAM memory and does not measurably impact performance.

A write process can be more complicated, particularly when data the host computer attempts to write is a subset of a physical 4K sector. In these cases, the hard drive must first read the entire 4K sector containing the targeted location of the host write request, merge the existing data with the new data and then rewrite the entire 4K sector (Figure 8).

In this instance, the hard drive must perform extra mechanical steps in the form of reading a 4K sector, modifying the contents and then writing the data. This process is called a read-modify-write cycle, which is undesirable because it has a negative impact on hard drive performance. Minimizing the probability and frequency of read-modify-write instances is the most important aspect of making the transition to 4K sectors smooth and painless.
Also see the sections from the link above regarding alignment.
Mar 21, 2015 at 5:07 PM
Edited Mar 21, 2015 at 5:23 PM
I understand about aligning, but VeraCrypt doesn't understand!
User (i'm user) use Volumes -> Create New Volume -> Encrypt a non system drive -> Choose Large drive ... Format it, Mount it - and this (Encrypted) Volume - not aligned and work very slow (in 8 times slower) !!!
VeraCrypt must create encrypted volume aligned to 4K sector.
No one utility can help, because Volume not standard - it's VeraCrypt encrypted volume. No one software cannot see and work with this volume.
Can You fix VeraCrypt Volume creation function?
Coordinator
Mar 21, 2015 at 6:09 PM
on Windows, VeraCrypt doesn't' support 4K sector size. There is an issue for this that was opened on February 1st: https://veracrypt.codeplex.com/workitem/85

The current code inherited from TrueCrypt assumes 512 bytes sector size all the time. In VeraCrypt, this was fixed for Linux and MacOSX but for Windows it is still ongoing because of the code complexity.

I'll update the ticket with news about the implementation. Meanwhile, you can vote for the issue to receive updates about it.
Mar 21, 2015 at 6:53 PM
Edited Mar 21, 2015 at 6:53 PM
Ok, I vote that ... (not much votes :( for now)
I have no problem with stability, only speed problem ...
Fast server drive work as slow old.