SSDs that support 512 byte sectors?

[cbn]

I found out that some applications like VMware VSphere 6.5 and VMware vSAN 6.5 6.6 don't support drives with 4K sectors:

https://blogs.vmware.com/virtualblo...mware-vsphere-6-5-now-supports-512e-drives-2/

https://kb.vmware.com/s/article/2091600

Do current GA versions of vSphere and VSAN support 4K Native drives?
No. 4K Native drives are not supported in current GA releases of vSphere and vSAN.

However some SSDs like the Intel P4800X (Optane) and S3500/S3700 can be converted to 512 byte sectors:

https://tinkertry.com/intel-isdct-r...vme-to-512e-to-use-under-esxi-65-vmfs-or-vsan

https://www.intel.com/content/www/us/en/support/articles/000006392/memory-and-storage.html

While this spec sheet for Crucial MX300 has 512 byte sector size support as one of the features.

Industry-standard, 512-byte sector size support

Samsung 840 Pro spec sheet:

https://www.samsung.com/us/pdf/memory-storage/840PRO_25_SATA_III_Spec.pdf (page 7)

Bytes per Sector
512 Bytes

Any other SSDs with 512 byte sectors or capable of 512 byte sectors?

 

[ashetos]

Every SSD that I know of is 512e. That means, 512-bytes logical sector size, 4KB physical sector size.

VMWare actually needs 512 bytes native sector size for performance reasons. VMWare performs 512-byte write I/O requests and 512e devices are doing a Read-Modify-Write operation, meaning they read 4KB, modify the 512-byte chunk and write 4KB, cause the controller can only do atomic operations at the 4KB level. That is also correct for most HDDs nowadays.

I believe VMFS 6.0 added 512e device support, meaning that the file-system will identify which devices have a physical sector size of 4KB and try to place most data at that alignment for performance reasons.

To summarize:
- logical sector size is what operating systems use as the minimum I/O size
- physical sector size is the actual sector size on the medium and has to do with performance and not correctness
- VMWare supports 512-byte native devices (logical sector size 512, physical sector size 512)
- VMWare does not support 4KB native devices (logical sector size 4096, physical sector size 4096)
- VMWare supports 512e devices for VMFS 6.0 (logical sector size 512, physical sector size 4096)
- most devices in the wild are 512e (HDDs and SSDs)
- VMWare works just fine with 512e devices for all versions but it's not officially supported for performance reasons

 

[cbn]

Thanks for your excellent post. That really cleared things up for me.

 

[thecoolnessrune]

As ashetos noted, vSAN 6.0 and higher supports 512e, so as long as you avoid 4K Native drives, you'll be fine. Both the SSDs you mentioned above would be fine, but are horrible for vSAN. You'll be crushed by write committals due to the lack of power loss protection. Definitely do not use them in the caching tier, and I wouldn't use them for the Capacity tier either.

If you have NVMe money and budget, get Optane 900P SSDs for the Caching Tier. Incredibly potent. If you don't have that kind of money, then at least get some old P3600, PM1725, or at least S3700 / Hitachi 100GB SLC SAS drives that have uniform write latency and power loss protection. Anything below that is literally throwing money away aside from the barest proof of concept (hey, it turns on).

 

[cbn]

As ashetos noted, vSAN 6.0 and higher supports 512e, so as long as you avoid 4K Native drives, you'll be fine. Both the SSDs you mentioned above would be fine, but are horrible for vSAN. You'll be crushed by write committals due to the lack of power loss protection. Definitely do not use them in the caching tier, and I wouldn't use them for the Capacity tier either.

If you don't have that kind of money, then at least get some old P3600, PM1725, or at least S3700 / Hitachi 100GB SLC SAS drives that have uniform write latency and power loss protection.

According this link the S3700 can change the physical sector size from 4K to 512 byte and vice versa:

https://www.intel.com/content/www/us/en/support/articles/000006392/memory-and-storage.html

So SSD with 512 byte physical and logical sector size vs. SSD with 4K physical Sector size and 512 logical sector size in VMWare? This compared to SAS 15K or 10K 2.5" HDD with 512 byte physical sectors (ie, not advanced format)?

From post #2 of this thread:

VMWare actually needs 512 bytes native sector size for performance reasons. VMWare performs 512-byte write I/O requests and 512e devices are doing a Read-Modify-Write operation, meaning they read 4KB, modify the 512-byte chunk and write 4KB, cause the controller can only do atomic operations at the 4KB level. That is also correct for most HDDs nowadays.

 

[thecoolnessrune]

According this link the S3700 can change the physical sector size from 4K to 512 byte and vice versa:

https://www.intel.com/content/www/us/en/support/articles/000006392/memory-and-storage.html

So SSD with 512 byte physical and logical sector size vs. SSD with 4K physical Sector size and 512 logical sector size in VMWare? This compared to SAS 15K or 10K 2.5" HDD with 512 byte physical sectors (ie, not advanced format)

From post #2 of this thread:

vSAN does perform a Read-Modify-Write operation. From the VMware KB: https://kb.vmware.com/s/article/2091600

4Kn is the advanced format in which the physical sectors and logical sectors are both 4,096 bytes in size.
512e is the advanced format in which the physical sector size is 4,096 bytes, but the logical sector size emulates 512 bytes sector size. The purpose of 512e is for the new devices to be used with OSs that do not support 4Kn sectors yet. However, inherently, 512-byte emulation involves a read-modify-write process in the device firmware for every write operation that is not 4KB aligned.

For example, a workload that does I/O operations that are either not aligned at a 4KB offset in bytes from the start of the disk or that are not 4KB multiples in length, one gets an alignment penalty caused by a read-modify-write process taking place in the drive for every write operation. The penalty is more pronounced for smaller operations. For larger I/Os, the per-operation latency is dominated by transfer times. Because many 512e drives are slightly faster than their older 512n counterparts, the alignment penalty is typically cancelled out after a certain operation size (say 256KB and larger, sometimes less).

In other words, even with 512e sectors, it is still preferable for the applications and the OS to perform 4KB aligned I/O for predicable performance. This is a general problem and not particular to any specific OS.

Especially in SSDs, most drives aren't writing and reading their advertised sector size. My old SSDs wrote / read at 8K, and I think many SSDs nowadays are 16K. It really doesn't matter that much as long as the reported sector size is right.

TL;DR: If you're for some reason using an old VMware version or stuck using VMFS5, then pay up for an expensive 512n SSD with PLP because VMware sucks sometimes. If you're using ESXi 6.5 and vSAN 6.6 with VMFS6 (as any new deployment should be), then get a 512e drive (which most SSDs will do, especially almost anything old enterprise), and be happy with it.[/QUOTE]