{"id":97454,"date":"2020-10-18T14:42:35","date_gmt":"2020-10-18T12:42:35","guid":{"rendered":"https:\/\/prohoster.info\/blog\/administrirovanie\/barery-i-zhurnaliruemye-fajlovye-sistemy"},"modified":"2020-10-18T14:42:35","modified_gmt":"2020-10-18T12:42:35","slug":"barery-i-zhurnaliruemye-fajlovye-sistemy","status":"publish","type":"post","link":"https:\/\/prohoster.info\/et\/blog\/administrirovanie\/barery-i-zhurnaliruemye-fajlovye-sistemy","title":{"rendered":"Logi ja ajalugu salvestavad failisysteemid","gt_translate_keys":[{"key":"rendered","format":"text"}]},"content":{"rendered":"
\n

Soovin k\u00f5igile head n\u00e4dalavahetust!<\/em><\/strong> Kutsume tasuta demotunnile <\/em>\u201eWebi serveri seadistamine (Apache, Nginx, Nginx'i tasakaalustamine)\u201c<\/em><\/a><\/noindex>, mida viib l\u00e4bi Andrei Buranov \u2014 UNIX-s\u00fcsteemide spetsialist Mail.Ru Group'is. Samuti avaldame artikli Jonathan Corbet'ilt \u2014 LWN.neti toimetajalt.<\/em><\/p>\n<\/blockquote>\n

Ajaloos salvestavad failisysteemid lubavad s\u00fcsteemiadministraatoreid vabastada ketta kahjustumise probleemidest s\u00fcsteemi t\u00f5rgete korral. Isegi ilma failis\u00fcsteemi terviklikkuse kontrollimise k\u00e4ivitamiseta. Kuigi tegelikkuses on k\u00f5ik veidi keerulisem. Ja nagu n\u00e4itab hiljutine arutelu, v\u00f5ib see olla isegi segasem, kui paljud meist arvavad, kuna ajaloos salvestavate failis\u00fcsteemide terviklikkuse tagamine m\u00f5jutab j\u00f5udlust.<\/p>\n

Failis\u00fcsteem, nagu ext3, kasutab ketas eraldi ala, mida nimetatakse \u017eurnaliks. Failis\u00fcsteemi metaandmete muudatuste tegemisel kirjutatakse need muudatused esmalt \u017eurnali ilma \u00fclej\u00e4\u00e4nud failis\u00fcsteemi muutmata. P\u00e4rast k\u00f5igi muudatuste salvestamist \u017eurnali lisatakse \u201ecommit block\u201c, mis n\u00e4itab tehingu l\u00f5petamist. Ja alles p\u00e4rast commit block'i salvestamist fikseeritakse tehing ja muudetud metaandmed salvestatakse kettale. Kui s\u00fcsteem mingil hetkel eba\u00f5nnestub, saab \u017eurnalis oleva teabe abil t\u00f6\u00f6 l\u00f5petada ja v\u00e4ltida failis\u00fcsteemi kahjustusi, kuna vaid osa metaandmeid on uuendatud.<\/p>\n

Siiski on \u00fcks komistus: failis\u00fcsteemi kood peab commit block'i kirjutamise eel olema t\u00e4iesti kindel, et kogu teave tehingu kohta on juba \u017eurnali j\u00f5udnud. Lihtsalt \u00f5igesse j\u00e4rjekorda kirjutamine ei ole piisav \u2014 t\u00e4nap\u00e4eva kettad toetavad suuri sisemisi vahem\u00e4lusid ja j\u00e4rjestavad operatsioone paremaks tootlikkuseks. Seet\u00f5ttu peab enne commit block'i selgelt n\u00e4itama, et k\u00f5ik \u017eurnali andmed tuleb kettale \u00fcle kanda. Kui commit block kirjutatakse varem, v\u00f5ib \u017eurnal kahjustuda. Selle probleemi lahendamiseks kasutatakse barj\u00e4\u00e4re. Sisuliselt keelab barj\u00e4\u00e4r kirjutada mingit plokki p\u00e4rast barj\u00e4\u00e4ri, kuni k\u00f5ik barj\u00e4\u00e4ri eelnevalt kirjutatud plokid on kettale \u00fcle kantud. Kasutades barj\u00e4\u00e4re, tagavad failis\u00fcsteemid failistruktuuride j\u00e4rjepidevuse.<\/p>\n

Kuid on veel \u00fcks probleem: ext3 ja ext4 failis\u00fcsteemid ei kasuta vaikimisi barj\u00e4\u00e4risid. Valik on olemas, kuid kui administraator ei l\u00fclita neid selges\u00f5naliselt sisse, siis t\u00f6\u00f6tavad need failis\u00fcsteemid ilma barj\u00e4\u00e4rideta, kuigi m\u00f5nes jaotuses (n\u00e4iteks SUSE) on vaikimisi v\u00e4\u00e4rtused teistsugused. Eric Sandeen otsustas hiljuti, et seda olukorda tuleb muuta ja tegi pat\u0161i<\/u><\/a><\/noindex>, mis muudab vaikimisi seadistusi ext3 ja ext4 jaoks. Ja siis algas elav arutelu.<\/p>\n

Andrew Morton vastas<\/u><\/a><\/noindex>, miks vaikimisi v\u00e4\u00e4rtus on just selline:<\/p>\n

\n

Eelmisel korral, kui me proovime seda muuta, halvenes paljude koormuste korral j\u00f5udlus 30%, seet\u00f5ttu viskasin ma k\u00f5ik need pat\u0161id kohkunult minema. Ma arvan, et me ei saa sellele minna ja aeglustada k\u00f5iki masinad nii t\u00f5siselt ...<\/em><\/p>\n

Siin pole ideaalset lahendust ja ma kaldun arvama, et ei tasu seda uinuvaid koera \u00e4ratada ja j\u00e4tta vaikimisi seaded jaotuste arendajate otsustada.<\/em><\/p>\n<\/blockquote>\n

Seet\u00f5ttu on vaikimisi barj\u00e4\u00e4rid v\u00e4lja l\u00fclitatud, kuna need m\u00f5juvad t\u00f5siselt tootlikkusele. Lisaks kasutatakse failis\u00fcsteeme \u00fcsna edukalt ilma barj\u00e4\u00e4rideta. Teated ext3 failis\u00fcsteemi kahjustumisest on haruldased ja v\u00e4hesed.<\/p>\n

Kuid see ei ole lihtsalt vedamine. Ted Ts'o selgitab<\/u><\/a><\/noindex> seda, et ext3 \/ ext4 ajalugu on tavaliselt pidevalt paigutatud. Esiteks, failis\u00fcsteemi draiver p\u00fc\u00fcab seda luua pidevana. Teiseks luuakse ajalugu tavaliselt koos failis\u00fcsteemiga, kui on lihtne leida pidevat ruumi. J\u00e4tkuvus ja j\u00e4rjestus on kasulikud mitte ainult j\u00f5udluse, vaid ka uuesti j\u00e4rjestuse t\u00f5kestamise jaoks. T\u00fc\u00fcpiline commit block paigutatakse kohe p\u00e4rast muid andmeid ajaloos, nii et kettal ei ole p\u00f5hjust uuesti j\u00e4rjestuse leidmiseks. Commit block kirjutatakse loomulikult kettale kohe p\u00e4rast muid ajaloos olevaid kandeid.<\/p>\n

Kuid keegi ei v\u00e4ida, et see alati nii j\u00e4\u00e4b. K\u00f5vakettad v\u00f5ivad k\u00e4ituda teisiti. Lisaks on \u017eurnal ringbuffer. Seega, kui tehing kirjutatakse \u017eurnali l\u00f5ppu, v\u00f5ib commit block sattuda varasemasse blokki, enne muid \u017eurnali kirjeid. Seega on kahjustamise oht alati olemas. Tegelikult on Chris Masonil selle kohta testid<\/u><\/a><\/noindex>. Pole kahtlust, et barj\u00e4\u00e4ridega t\u00f6\u00f6tamine on v\u00e4hem turvaline kui nende puudumine.<\/p>\n

Kui olete valmis suutma j\u00f5udluse kahjustust, siis v\u00f5ite barj\u00e4\u00e4rid sisse l\u00fclitada. Kuid ainult juhul, kui teie failis\u00fcsteem ei p\u00f5hine LVM-il (nagu m\u00f5nes jaotuses vaikimisi). Tundub, et seadme kaardistaja ei toeta barj\u00e4\u00e4re. Muudel juhtudel oleks hea v\u00e4hendada j\u00f5udluse langust. Ja n\u00e4ib, et seda on v\u00f5imalik teha.<\/p>\n

Praegune ext3 rakendus (kui barj\u00e4\u00e4rid on sisse l\u00fclitatud) t\u00e4idab iga tehingu jaoks j\u00e4rgmised toimingud:<\/p>\n

    \n
  1. \n

    Andmed kirjutatakse \u017eurnali<\/p>\n<\/li>\n

  2. \n

    Teostatakse barj\u00e4\u00e4r<\/p>\n<\/li>\n

  3. \n

    Kirjutatakse commit block<\/p>\n<\/li>\n

  4. \n

    Teostatakse j\u00e4rgmine barj\u00e4\u00e4r<\/p>\n<\/li>\n

  5. \n

    Hiljem kirjutatakse metaandmed kettale<\/p>\n<\/li>\n<\/ol>\n

    ext4 failus\u00fcsteemis saab esimesest takistuspunktist (samm 2) loobuda, kuna ext4 toetab ajakirjade kontrollsummasid.<\/p>\n

    Kui ajakirja andmed ja commiti plokk on \u00fcmber korraldatud ning operatsioon katkestatakse t\u00f5rke t\u00f5ttu, siis ajakirja kontrollsumma ei vasta sellele, mis on salvestatud commiti plokis, ja tehingut ei aktsepteerita. <\/p>\n

    Chris Mason usub<\/u><\/a><\/noindex>, \u00fctles, et oleks \u201e\u00fcldiselt ohutu\u201c eemaldada see barj\u00e4\u00e4r ka ext3-st, v\u00e4lja arvatud juhul, kui \u017eurnal j\u00f5uab l\u00f5puni ja hakkab kirjutama algusest peale. <\/p>\n

    Veel \u00fcks idee, et suurendada toimivust, on takistuste opereerimise edasi l\u00fckkamine, kui see on v\u00f5imalik. Kui andmete kohe kettale kirjutamine ei ole h\u00e4davajalik, siis v\u00f5idakse ajakirjas luua mitu tehingut ja need kettale \u00fche takistusega kirjutada.<\/p>\n

    Samuti on teatud potentsiaal parendamiseks, hoolika tegevuste j\u00e4rjestamise kaudu, et barj\u00e4\u00e4rid (mida tavaliselt rakendatakse kui \u201ek\u00f5ik ootel olevad operatsioonid kettale t\u00fchjendada\u201c taotlused) ei sunniks kirjutama plokke, millel ei ole j\u00e4rjestust.<\/p>\n

    Tundub, et on aeg m\u00f5elda, kuidas muuta takistuste maksumus vastuv\u00f5etavaks. Ted Ts'o paistab olevat samuti selliselt arvanud<\/u><\/a><\/noindex>:<\/p>\n

    \n

    Ma arvan, et peaksime ext3\/4 sisse panema barj\u00e4\u00e4rid ja seej\u00e4rel t\u00f6\u00f6tama ext4\/jbd2 \u00fclehead kulude v\u00e4hendamise nimel. T\u00f5en\u00e4oliselt ei t\u00f6\u00f6ta enamik s\u00fcsteeme tingimustes, nagu Chris kasutas probleemi demonstreerimiseks, ja faili s\u00fcsteemi turvalisus peaks olema prioriteet.<\/em><\/p>\n<\/blockquote>\n

    Mulle \u00fctleb terve m\u00f5istus, et see koer ei maga enam ja t\u00f5en\u00e4oliselt hakkab ta m\u00f5nda aega h\u00e4\u00e4lt tegema. See v\u00f5ib tekitada m\u00f5ningate naabrite seas muret, kuid see on parem kui lasta tal hammustada.<\/p>\n

    Kas oled huvitatud selle valdkonna arengust?<\/em><\/strong> Registreeru tasuta Demo-tundi <\/em>\u201eWebi serveri seadistamine (Apache, Nginx, Nginx'i tasakaalustamine)\u201c<\/em><\/a><\/noindex> ja osale \u00fclekandes <\/em>\u201eT\u00f6\u00f6tamine logidega Linuxis\u201c<\/em><\/a><\/noindex>, mida viib l\u00e4bi Pavel Viki\u0155\u00fck \u2014 MVNO sideoperaator, DevOps-insener. <\/em><\/p>\n

    Allikas: habr.com<\/a> <\/p>","protected":false,"gt_translate_keys":[{"key":"rendered","format":"html"}]},"excerpt":{"rendered":"

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