Re: [linux-lvm] bcache now to become io-manager?
Dne 31. 10. 19 v 20:29 John Stoffel napsal(a): "Joe" == Joe Thornber writes: Joe> On Tue, Oct 29, 2019 at 08:25:23PM -0400, John Stoffel wrote: "Joe" == Joe Thornber writes: [ I saw this and couldn't resist asking for more details ...] Joe> Also there are big changes to bcache coming, that remove file Joe> descriptors from the interface completely. See the branch Joe> 2019-09-05-add-io-manager for more info (bcache has been renamed Joe> io_manager). Can you post the full URL for this, and maybe give us a teaser on what to expect? I run lvache on my home system and I'd love to know how to A) improve reporting of how well it works, and B) whether I'm using it right, and of course C) if bcache would be a better replacement. I'm using Linux v5.0.21 (self compiled) on Debian 9.11 with lvcache setup. It's a pair of mirrored 250gb SSDs in front of 4tb of mirrored disk. So anything where I can use my SSDs to cache my data accesses is certainly interesting. Joe> Sorry, I think we're getting confused with similarly named Joe> things. There is a component in LVM source called 'block cache' Joe> that we use to scan devices in parallel (under the hood it uses Joe> aio). That component is being renamed. It's nothing to do with Joe> the disk caching technology called 'bcache'. Ah... that's a good reason for this rename then. In this context bcache is purely an internal lvm2 coding naming - it's never exposed to an lvm2 man page, never used as any argument or parameter in lvm2 command line - so it really is purely terminology for coders... Joe> However, Dave Teigland has been adding support to LVM for a new Joe> caching target that emphasises caching writes. So keep an eye Joe> out for that. Will do. It's never really been clear if lvcache has really helped or not, the testing was in-conclusive. dm-cache (aka 'lvcreate --cache') is a hotspot cache - so it does 'monitor' your device usage and moves to caching device hotspot areas (those which are frequently used). And there need to be seen that often there is also hidden 'page-cache' usage which avoids increasing usage of real disk reads - so it simply takes times before dm-cache gets well populated - this is something you could hardly 'benchmark' with like couple minutes long benchmark. The recently introduced dm-writecache (aka 'lvconvert --type writecache) support on the other hand looks more or less like 'extended' page-caching - where all dirty pages from memory quickly lends in fast write caching device where they are copied to your slower physical storage device. Regads Zdenek ___ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
Re: [linux-lvm] bcache now to become io-manager?
> "Joe" == Joe Thornber writes: Joe> On Tue, Oct 29, 2019 at 08:25:23PM -0400, John Stoffel wrote: >> > "Joe" == Joe Thornber writes: >> >> [ I saw this and couldn't resist asking for more details ...] >> Joe> Also there are big changes to bcache coming, that remove file Joe> descriptors from the interface completely. See the branch Joe> 2019-09-05-add-io-manager for more info (bcache has been renamed Joe> io_manager). >> >> Can you post the full URL for this, and maybe give us a teaser on what >> to expect? I run lvache on my home system and I'd love to know how to >> A) improve reporting of how well it works, and B) whether I'm using it >> right, and of course C) if bcache would be a better replacement. >> >> I'm using Linux v5.0.21 (self compiled) on Debian 9.11 with lvcache >> setup. It's a pair of mirrored 250gb SSDs in front of 4tb of mirrored >> disk. >> >> So anything where I can use my SSDs to cache my data accesses is >> certainly interesting. Joe> Sorry, I think we're getting confused with similarly named Joe> things. There is a component in LVM source called 'block cache' Joe> that we use to scan devices in parallel (under the hood it uses Joe> aio). That component is being renamed. It's nothing to do with Joe> the disk caching technology called 'bcache'. Ah... that's a good reason for this rename then. Joe> However, Dave Teigland has been adding support to LVM for a new Joe> caching target that emphasises caching writes. So keep an eye Joe> out for that. Will do. It's never really been clear if lvcache has really helped or not, the testing was in-conclusive. John ___ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
Re: [linux-lvm] bcache now to become io-manager?
On Tue, Oct 29, 2019 at 08:25:23PM -0400, John Stoffel wrote: > > "Joe" == Joe Thornber writes: > > [ I saw this and couldn't resist asking for more details ...] > > Joe> Also there are big changes to bcache coming, that remove file > Joe> descriptors from the interface completely. See the branch > Joe> 2019-09-05-add-io-manager for more info (bcache has been renamed > Joe> io_manager). > > Can you post the full URL for this, and maybe give us a teaser on what > to expect? I run lvache on my home system and I'd love to know how to > A) improve reporting of how well it works, and B) whether I'm using it > right, and of course C) if bcache would be a better replacement. > > I'm using Linux v5.0.21 (self compiled) on Debian 9.11 with lvcache > setup. It's a pair of mirrored 250gb SSDs in front of 4tb of mirrored > disk. > > So anything where I can use my SSDs to cache my data accesses is > certainly interesting. Sorry, I think we're getting confused with similarly named things. There is a component in LVM source called 'block cache' that we use to scan devices in parallel (under the hood it uses aio). That component is being renamed. It's nothing to do with the disk caching technology called 'bcache'. However, Dave Teigland has been adding support to LVM for a new caching target that emphasises caching writes. So keep an eye out for that. - Joe ___ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
[linux-lvm] bcache now to become io-manager?
> "Joe" == Joe Thornber writes: [ I saw this and couldn't resist asking for more details ...] Joe> Also there are big changes to bcache coming, that remove file Joe> descriptors from the interface completely. See the branch Joe> 2019-09-05-add-io-manager for more info (bcache has been renamed Joe> io_manager). Can you post the full URL for this, and maybe give us a teaser on what to expect? I run lvache on my home system and I'd love to know how to A) improve reporting of how well it works, and B) whether I'm using it right, and of course C) if bcache would be a better replacement. I'm using Linux v5.0.21 (self compiled) on Debian 9.11 with lvcache setup. It's a pair of mirrored 250gb SSDs in front of 4tb of mirrored disk. So anything where I can use my SSDs to cache my data accesses is certainly interesting. John ___ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
