[HN Gopher] LVM Cache Surprises
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       LVM Cache Surprises
        
       Author : JNRowe
       Score  : 34 points
       Date   : 2022-03-07 13:00 UTC (10 hours ago)
        
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       | mfontani wrote:
       | I've been debugging a sporadic high IO wait time very recently,
       | and we ended up tuning vm.dirty_ratio and
       | vm.dirty_background_ratio. I wonder whether those were already
       | tuned from the very high % of ram default, or whether it could
       | have any impact here.
        
       | ColonelPhantom wrote:
       | I use lvmcache for my desktop, which has an old and tiny SSD
       | (most of which is given to Windows) but a large HDD. Performance
       | can be unpredictable at times, but is generally quite good.
        
       | antongribok wrote:
       | I have about 50-100 PB of object storage workloads sitting on top
       | of LVM cache for the past 5 years or so in production. It works
       | extremely well.
       | 
       | Before going into prod, we tested LVM cache, and bcache, and LVM
       | cache worked better for our workloads. Also, the tooling is
       | significantly better than bcache.
       | 
       | One thing I love about LVM cache is if you are already running
       | with LVM, you can add the caching layer on the fly without any
       | downtime.
       | 
       | Regarding the note at the end where the author sees poor
       | performance. I recommend taking a very close look at the SSD
       | model. I've seen enterprise SSDs that perform worse with sync IO
       | than spinning disks. When we buy hardware, we tell our vendors
       | the exact model of SSD they can use. If we haven't qualified the
       | SSD, we don't put it in production.
        
         | quadrature wrote:
         | Could you expand a bit on what your use case is ?. Is this a
         | cache in front of an s3 data warehouse or something like that
         | ?.
        
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       (page generated 2022-03-07 23:01 UTC)