3 ms·
I am referring to physical pages in an SSD disk. The 8k pg page maps to 2 pages in a typical SSD disk. Your comment proves my initial point, which is write ampl
by halayli 2y ago
I am referring to physical pages in an SSD disk. The 8k pg page maps to 2 pages in a typical SSD disk. Your comment proves my initial point, which is write amplification cannot be discussed without talking about the disk types and their behavior.
- emptiestplace 2y agoHuh? It seems you've forgotten that you were just saying that a single bit change would result in a 4096 byte write.
- Tostino 2y ago> a single bit change would result in a 4096 byte write On (most) SSD hardware, regardless of what software you are using to do the writes. At least that's how I read their comment.
- emptiestplace 2y agoRight, and if pg writes 8192 bytes every time, this is no longer relevant.
- mschuster91 2y ago> The 8k pg page maps to 2 pages in a typical SSD disk. You might end up with even more than that due to filesystem metadata (inode records, checksums), metadata of an underlying RAID mechanism or, when working via some sort of networking, stuff like ethernet frame sizes/MTU. In an ideal world, there would be a clear interface which a program can use to determine for any given combination of storage media, HW RAID, transport layer (local attach vs stuff like iSCSI or NFS), SW RAID (i.e. mdraid), filesystem and filesystem features what the most sensible minimum changeable unit is to avoid unnecessary write amplification bloat.
- emptiestplace 2y agoBut they are usually separate: an 8192 byte write does fit neatly get into two 4096-byte pages, and metadata writes, while also subject to write amplification, typically occur separately and can represent multiple data blocks.