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From: Mateusz Korniak <mateusz-lists@ant.gliwice.pl>
To: Thomas Fjellstrom <thomas@fjellstrom.ca>
Cc: linux-raid@vger.kernel.org
Subject: Re: Best option for SSD caching on a md raid array?
Date: Mon, 08 Feb 2016 10:38:40 +0100	[thread overview]
Message-ID: <7465555.90dcXqM3S1@matkor-toshiba> (raw)
In-Reply-To: <1670804.QnHtKWfib8@nell>

On Sunday 07 February 2016 22:14:08 Thomas Fjellstrom wrote:
> I'm wondering what the "best" route for me to go is. There's a few options
> that I know of, like flashcache, dm-cache, and bcache. The question is which
> of those is better suited to my use case?

bcache cons:
- no maintainer, bugs living years
- partition have to be formatted as bcache

lvmcache cons:
- in case of failure of caching device, whole cache volume stops working (data 
is not lost though).
- cumbersome way of removing cache from LV when caching device is not 
accessible/failed.

lvmcache pros:
- One can turn on/off caching for active/mounted LV.

We moved from bcache to lvmcache (knowing it's limitations) using write-
through mode and for more-reads-than-writes DB access patterns [1].


[1]: Examble postgresql load (sdc is caching SSD, over sda/b RAID10).
Device:         rrqm/s   wrqm/s     r/s     w/s    rMB/s    wMB/s avgrq-sz 
avgqu-sz   await r_await w_await  svctm  %util
sda               0.00    33.93    0.07  179.13     0.00     3.38    38.59     
6.23   34.75   23.50   34.76   2.63  47.07
sdb               0.00    35.97    0.03  177.17     0.00     3.38    39.04     
9.57   53.99  337.00   53.94   2.97  52.66
sdc               8.03     2.63  631.07  201.13     6.04     3.35    23.10     
0.19    0.23    0.19    0.35   0.15  12.34



Regards,
-- 
Mateusz Korniak
"(...) mam brata - poważny, domator, liczykrupa, hipokryta, pobożniś,
 	krótko mówiąc - podpora społeczeństwa."
				Nikos Kazantzakis - "Grek Zorba"

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  parent reply	other threads:[~2016-02-08  9:38 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-02-08  5:14 Best option for SSD caching on a md raid array? Thomas Fjellstrom
2016-02-08  8:36 ` David Brown
2016-02-08 15:45   ` Jens-U. Mozdzen
2016-02-08 20:21   ` Thomas Fjellstrom
2016-02-08  9:38 ` Mateusz Korniak [this message]
2016-02-08 15:34 ` John Stoffel
2016-02-10 22:13   ` Pasi Kärkkäinen
2016-02-10 22:21     ` John Stoffel
2016-02-10 22:54       ` Pasi Kärkkäinen

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