Re: IIs factible to implement full writes of strips to raid using NVRAM memory in LFS?

[Bert Kiers <kiers%original.xs4all.nl@localhost>]

On Thu, Aug 18, 2016 at 07:58:53PM +0200, Jose Luis Rodriguez Garcia wrote:

Hi,

> As I understand LFS needs to do synchronous writes when there is
> metadata operations (directories)/fsync operations involved. Instead
> of writting a full segment (1 MB per default), it writes a "small
> segment". It kills performance in RAID 5/6, because the write isn't a
> full stripe: you have to read all the disks, for calculate the new
> parity 1 write on raid of x disks= x reads + 2 writes (data + parity).
> 
> The NVRAM memory solves this problem as buffer/ write cache.

Sounds like WAFL https://en.wikipedia.org/wiki/Write_Anywhere_File_Layout

Even though that article doesn't mention NVRAM, all Netapp filers have
a (fixed) amount of NVRAM.

Our big FAS8080 has 16384 MB NVRAM, the small FAS2554 has 2 GB NVRAM. 
Writes are very fast.

Grtnx,
-- 
B*E*R*T