[Nottingham] RAID stripe size?
martin at ml1.co.uk
Thu Sep 29 11:04:08 UTC 2011
Summary for the 'executive view' :-)
On 29 September 2011 12:01, Martin <martin at ml1.co.uk> wrote:
> An interest here is that all new HDDs as of January this year are
> manufactured with the new 4kByte physical sectors rather than the old
> 512Byte sectors. They transparently maintain 512Byte sector
> compatibility by performing a read-modify-writes as needed, but at a
> high performance cost...
> Trying to guess some real world numbers:
> Hence as a guess... For HDDs depending on application, chunks of
> 64kByte to 256kByte;
> For SSDs I'd guess go right down to the write page size of 4kBytes.
> Note that for SSDs, the 4kByte read/write performance is usually given
> as /the/ headline (best) spec. Also, for performance charts I've seen,
> SSDs max out on their read/write data rate at about the 1kByte IO
> read/write size in any case.
> And then... For btrfs for SSDs, that suggests formatting with:
> mkfs.btrfs -L SSD_label_name -s 4096 /dev/sdX
> or for 16kByte write pages:
> mkfs.btrfs -L SSD_label_name -s 16384 /dev/sdX
> (And btrfs can implement it's own "RAID" at the filesystem level)
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