Any maintained alternative for flashcache? Is flashcache still useable?

vmunich

I host a a few hundred sites in my cPanel server. They don't have a lot of traffic but they need quite a bit of disk space (photographing sites with hundreds of large images).

Running these sites entirely off a pure SSD raid1 setup will be expensive, I need at least 2TB of disk space.

My current server has a 2x4TB 7200rpm disks raid1 + 2x250gb SSD raid1. /home is mounted in the HDD raid, and everything else (OS, databases) is in the SSD raid.

I wanna setup some sort of SSD caching. Flashcache seems to be the easiest to setup, but it is deprecated and is no longer maintained. Should I still use it? Or maybe an alternative? I'm reading about bcache, but apparently I'd need to format my existing partitions and that won't be possible.

raindog308

vmunich said: I wanna setup some sort of SSD caching

If you have 2TB of images and the typical visitor views a wide assortment of them, I wonder if caching will help.

OTOH if the newest 1% are 80% of your traffic, different story.

WSS

Bcachefs?

rm_

lvmcache works pretty nicely, just set it up for my RAID arrays at home.

Bcache is half baked shit, and Bcachefs doesn't inspire confidence since it's from the same author.

flatland_spider

dm-cache and lvmcache, which is based on dm-cache, look like the two options after some searching.

vmunich

From my researching it looks like lvmcache is the way to go as well. Was wondering if it was what people were using. I'll check it out thanks

jackb

If you go with lvmcache and want to cache sequential IO, be aware it avoids that by default (see sequential_threshold).

rm_

jackb said: If you go with lvmcache and want to cache sequential IO, be aware it avoids that by default (see sequential_threshold).

That's for the older "mq" caching policy, the new one "smq" is entirely automatic and doesn't use that setting. I suppose you would still use mq if you run an older kernel, but from what I read it performed so much worse than smq.

jackb

@rm_ said:

jackb said: If you go with lvmcache and want to cache sequential IO, be aware it avoids that by default (see sequential_threshold).

That's for the older "mq" caching policy, the new one "smq" is entirely automatic and doesn't use that setting. I suppose you would still use mq if you run an older kernel, but from what I read it performed so much worse than smq.

Interesting, I spotted it (spinner performance for sequential io) testing on CentOS7. I'll check out which policy it uses next time I'm looking at it

vmunich

I'm having a hard time finding any good guide or explaining on lvmcache. Would it work on CentOS 6.8? Can anyone point me to some good resources?

Thanks

jackb

@vmunich said:
I'm having a hard time finding any good guide or explaining on lvmcache. Would it work on CentOS 6.8? Can anyone point me to some good resources?

Thanks

Man page is a good start. Here's an online copy.

http://man7.org/linux/man-pages/man7/lvmcache.7.html

Yes, it should work on centos 6.8 given a recent version of lvm2.