4K Advanced Format Hard Disks – Align or not to align for my NAS?
I guess you have heard about Advanced Format hard disks – large capacities hard disks that utilizes 4KB data sectors instead of 512B sectors. Advanced Format uses storage surface area more efficiently, allowing manufacturers to roll out higher density disk platters. This is because 4KB (4096B) with ECC block takes far less real estate on the disk platter than eight 512B with ECC blocks.
How does it impact my NAS?
However, NAS (Network Attached Storage) nowadays are designed with 512B data sectors in mind. What impact does it have?
For read operations, the emulation layer reads the entire 4096B block and reformat it into chunks of512B before sending to the NAS. This probably means no impact to the performance as advanced format disks usually come with larger cache.
For write operations, the NAS issues 512B data writes to the advanced format disk, the hard disk waits for eight chunks of 512B data (to form one 4KB data) before writing it to the disk. If the 4KB data does not align with the 4KB boundary on the disk surface, the NAS may suffer a performance impact as it requires additional spin of the disk platter compared to a aligned disk which completes the write in the first spin.
So if the NAS doesn’t align the partitions with the 4KB boundary, potentially the NAS suffers penalty during write operations.
How do I know my NAS is affected?
If you are able to look at the partition information on the hard disk. Take note of the starting block of each partition. If the number is not a multiple of 4, it means that it is not aligned. Below I have a 2TB disk (in my D-Link DNS-320) that is not aligned to the 4KB boundary. The starting blocks are 63, 2088450 and 1060290 for partitions sda1, sda2 and sda4 respectively. These numbers are not multiples of 4.
/ # fdisk -lu
Disk /dev/sda: 2000.3 GB, 2000398934016 bytes
255 heads, 63 sectors/track, 243201 cylinders, total 3907029168 sectors
Units = sectors of 1 * 512 = 512 bytes
Disk identifier: 0x1b8afeccDevice Boot Start End Blocks Id System
/dev/sda1 63 1060289 530113+ 82 Linux swap / Solaris
/dev/sda2 2088450 3904983809 1951447680 83 Linux
/dev/sda4 1060290 2088449 514080 83 Linux
If you are concerned about your new storage investment, align the disks/data partitions. I can’t guarantee that there will be significant write improvements but experiments by geeks have shown improvements! Some is better than nothing!
Want to align your disks (in your NAS)?
I will be writing a simple set of guide to re-align the standard (non-RAID) disks for fonz’s fun_plug enabled NAS (e.g. D-Link DNS-323, DNS-320, etc). Look out for it. 🙂
Getting a DNS-320 or Samsung F4 2TB HDD?
Check out D-Link Systems ShareCenter 2-Bay USB 2.0 External Hard Drive Enclosure DNS-320 Black
and Samsung Spinpoint F4EG 2 TB SATA2 5400rpm 32 MB Hard Drive HD204UI/Z4 deals on Amazon.com