Path: csiph.com!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail From: Peter Chant Newsgroups: comp.os.linux.hardware Subject: Re: Speed ups for a disk IO bound machine Date: Sat, 10 Dec 2016 20:44:04 +0000 Lines: 63 Message-ID: References: <5b6thd-pt2.ln1@lazy.lzy> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit X-Trace: individual.net mpTDYQVeu1HMCjV5QQTtkQ/6vKXcSl82DcbDXhFtPDPp1qnf4= Cancel-Lock: sha1:lUVz5H9WNcqILe7PeuDPAsc0gLw= User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 In-Reply-To: <5b6thd-pt2.ln1@lazy.lzy> Xref: csiph.com comp.os.linux.hardware:3246 On 12/10/2016 11:43 AM, Piergiorgio Sartor wrote: > On 2016-12-07 23:41, Peter Chant wrote: > [...] >> Any thoughts? > > First of all, it would be good to know which kind > of I/O is occuring. > Is streaming read or write? > Is random read or write? Well, I've not taken any formal stats but a good part of the load is mariadb at the same time as apache / php and firefox. I'd assume random. It looks like the mechanical drives are the ones with the biggest noticeable usage. The system SSD shows > > In general, I usually would suggest to use 2 SSD > in RAID-10 (Linux md). > This will double the streaming read performance and, > to certain extent, the random one. > The write performance will be the same as 1 SSD. I'm a bit confused here. My understanding is that RAID10 requires four disks, that they are striped in pairs and the pairs then mirror each other. So I can't do that if I have two drives. > > Same for the HDDs, but possibly with some SSD (over > RAID-10) caching. > This because writing might be a bit slower (actually > the FS RAM cache makes this not too observable). > Again I have two hdds. Raid10 with two SSDs and two HDDs would not make sense to me, and I'm not convinced you are suggesting that. So perhaps I've misunderstood. This has got me thinking, rather than putting in the spare SSD only for maria db I could bcache both HDDs. Though I wince a bit at the lack of symmetry in practice the drive with the system on it seems lightly used and it is much larger. If I get a SATA III controller that would speed it up possibly offsetting any performance loss. I'd still keep the main system on a non-cached ssd only portion to keep boot devices much simpler. > In this case, the question is if it is better to use > bcache or lvmcache. > This depend on the load. The second is an "hotspot" > cache, meaning blocks frequently accessed are cached. > The first is a more generic cache. > Depending on use cases, one is better than the other. > Hmm. bcache is simpler as a starting point. > Hope this helps, > > bye, > Thanks.