Date: Fri, 28 Mar 2014 23:36:33 -0500 From: Karl Denninger <karl@denninger.net> To: freebsd-fs@freebsd.org Subject: Re: zfs l2arc warmup Message-ID: <53364DD1.6040100@denninger.net> In-Reply-To: <alpine.BSF.2.00.1403290141300.60856@woozle.rinet.ru> References: <CAFfb-hpi20062%2BHCrSVhey1hVk9TAcOZAWgHSAP93RSov3sx4A@mail.gmail.com> <CALfReydi_29L5tVe1P-aiFnm_0T4JJt72Z1zKouuj8cjHLKhnw@mail.gmail.com> <CAFfb-hpZos5-d3xo8snU1aVER5u=dSFRx-B-oqjFRTkT83w0Kg@mail.gmail.com> <20140328005911.GA30665@neutralgood.org> <CAFfb-hr=wR6nxqL%2B4tn-y2eQEw4n_g7rZoK9rRLnm_Ldcm1TZQ@mail.gmail.com> <alpine.BSF.2.00.1403290032070.60856@woozle.rinet.ru> <CAOjFWZ7h5080%2BzEvSfzxgENwP%2BPXEXKPXdEDHAtbx5RAxxWT0g@mail.gmail.com> <alpine.BSF.2.00.1403290116550.60856@woozle.rinet.ru> <33ff828c517307c9681c361a12cff2ee@mail.mikej.com> <alpine.BSF.2.00.1403290141300.60856@woozle.rinet.ru>
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[-- Attachment #1 --] On 3/28/2014 4:45 PM, Dmitry Morozovsky wrote: > On Fri, 28 Mar 2014, mikej wrote: > >>> [snip most again] >>> >>>> Around ZFSv14-ish, the ability to import a pool with a missing ZIL was >>>> added. >>>> >>>> Remember the flow of data in ZFS: >>>> async write request --> TXG --> disk >>>> sync write request --> ZIL >>>> \--> TXG --> disk >>>> >>>> All sync writes are written to the pool as part of a normal async TXG >>>> after >>>> its written sync to the ZIL. And the ZIL is only ever read during pool >>>> import. >>> On the other side, doesn't it put the risk on sync-dependent, like database, >>> systems? >>> >>> I'm thinking not about losing the transaction, but possibly putting your >>> filesystem in the middle of (database PoV) transaction, hence render your DB >>> inconsistent? >>> >>> Quick googling seems to be uncertain about it... >> As I understand it..... (And I am always looking for an education) >> >> Any files system that honors fsync and provided the DB uses fsync should be >> fine. >> >> Any data loss then will only be determined by what transaction (log) >> capabilities the DB has. > And? > > 1. The DB issues "sync WAL" request, which is translated to fsync-like FS > requests, there are (IIUC) should ne directed to ZIL. > > 2. ZIL is failing in the middle of the request, or, even more bad, after > reporting that ZIL transaction is done, but before translating ZIL to the > underlying media > > 3. inconsistend DB? > > I'm in hope I'm wrong somewhere... If the DB is EVER lied to on a fsync'd write (that is, it gets back completion when the write was not actually complete and on stable storage) you're asking for a corrupted database. It doesn't much matter WHY the DB was lied to. All modern database systems rely on the filesystem and operating system NOT lying to them about the fact that data written is on stable storage when a fsync'd write call returns. -- -- Karl karl@denninger.net [-- Attachment #2 --] 0 *H 01 0 + 0 *H O0K030 *H 01 0 UUS10UFlorida10U Niceville10U Cuda Systems LLC1 0UCuda Systems LLC CA1/0- *H customer-service@cudasystems.net0 130824190344Z 180823190344Z0[1 0 UUS10UFlorida10UKarl Denninger1!0 *H karl@denninger.net0"0 *H 0 bi՞] MNԿawx?`)'ҴcWgR@BlWh+ u}ApdCF JVй~FOL }EW^bچYp3K& ׂ(R lxڝ.xz?6 &nsJ +1v9 v/( kqĪp[vjcK%fϻe?iq]z lyzFO'ppdX//Lw(3 JI A*S#՟H[f|CGqJKoo y.oEuOw$ /섀$삻J9b|A P~8]D1YI<"""Y^T2iQ2 b yH)] Ƶ0y$ _N 6XqMC 9 XgώjGTP"#nˋ"Bk1 00 U 0 0 `HB0 U 0, `HB OpenSSL Generated Certificate0 U |8 ˴d[20 U #0]Af4 U3x&^"408 `HB+)https://cudasystems.net:11443/revoked.crl0 *H gBwH] j\x`( &gW32"Uf^. ^Iϱ k!DQA g{(w /)\N'[ oRW @C HO>)XrTNɘ!u`xt5(=f\-l3<@C6mnhv##1ŃbH͍_Nq aʷ?rk$^9TIa!kh,D -ct1 0001 0 UUS10UFlorida10U Niceville10U Cuda Systems LLC1 0UCuda Systems LLC CA1/0- *H customer-service@cudasystems.net0 + ;0 *H 1 *H 0 *H 1 140329043633Z0# *H 1a ;\;iA 0l *H 1_0]0 `He*0 `He0 *H 0*H 0 *H @0+0 *H (0 +71001 0 UUS10UFlorida10U Niceville10U Cuda Systems LLC1 0UCuda Systems LLC CA1/0- *H customer-service@cudasystems.net0 *H 101 0 UUS10UFlorida10U Niceville10U Cuda Systems LLC1 0UCuda Systems LLC CA1/0- *H customer-service@cudasystems.net0 *H Wtҍ4%M)J`HQ>qߧ) ]Ss&x@?Ӻӓ9@%Sg00L8IŨJB ^ꬓ*D:; };Lm[@wۈCrRდ= 0n_uhX ]0褽6)@G#ŽL0V0P+"yB)Q c<]~:vgõhE9'U_aPڴKu{Q{ꃽȇ T4 <7[ %QOrSG$ xVQ{> ۶ም0F| FO-9+~ZkIWH5Q%qy"/ZWA jiI H[K9ιJ64PʀrVb#X+uV> =ij?>lUOO/ҷ%YdbEH|Lv+^oCI*dI A2pB)iI
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