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https://issues.apache.org/jira/browse/TS-745?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13662684#comment-13662684
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John Plevyak commented on TS-745:
---------------------------------
I think the idea of stealing bits from the directory which are hard coded to
point off device (off the hard disk which the directory is a part of) is a huge
design departure and a problem. When the cache was first built, it was limited
to 8GB disks which seemed HUGE. For Apache I extended it to .5PB as by then
8GB was far too small. Currently disks are at 4TB and this patch would
decrease the limit from .5PB to 32TB which gives us only a few years headroom,
not a good idea. Furthermore, the current design let's you unplug any cache
disk from any machine, move it to another machine and have your cache back.
This change stores SSD information in the HDD directory! why? Changing the
configuration, a disk or machine failure, etc. invalidates that information
corrupting the cache. Why not store that information in a side structure and
either store it only in memory only or on the SSD?
The idea of storing the SSD configuration in a string in records.config is also
a bad idea.
Overall, a stacked cache seems like a better idea or a minimally invasive
extension would be great. This patch is pretty invasive, duplicates code and
generally touches many bits of the code. The ram cache for example uses no
bits in the HDD directory and only a couple entry points at well defined places
(insert, lookup and delete/invalidate).
This patch looks to incur more technical depth at a time when I think we would
like to decrease the technical debt. For example, it would be nice to have
more smaller locks, move the HTTP support out of the core via a well defined
interface, add layering, etc. Adding yet another set of core code paths is
going to make those changes harder.
my 2 cents.
> Support ssd
> -----------
>
> Key: TS-745
> URL: https://issues.apache.org/jira/browse/TS-745
> Project: Traffic Server
> Issue Type: New Feature
> Components: Cache
> Reporter: mohan_zl
> Assignee: weijin
> Fix For: 3.3.5
>
> Attachments: 0001-TS-745-support-interim-caching-in-storage.patch,
> ts-745.diff, TS-ssd-2.patch, TS-ssd.patch
>
>
> A patch for supporting, not work well for a long time with --enable-debug
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