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5. To NFS mesw argwn grammwn

Oi arges grammes perilambanoyn ta modems, to ISDN, kai pi8anotata alles syndeseis makrwn apostasewn.

Ayto to tmhma basizetai se gnwseis sxetika me ta xrhsimopoioumena prwtokolla, alla oxi se pragmatikes peiramatikes dokimes. Parakalw, enhmerwste me, an dokimasete ta parakatw! ;-)

To prwto pragma poy prepei na 8ymaste, einai pws to NFS einai argo prwtokollo. Exei megalh eisagwgh. To na xrhsimopoieis to NFS gia na metafereis arxeia, einai sxedon sa na xrhsimopoieis to prwtokollo kermit. Einai argo. Sxedon opoiodhpote allo einai taxutero toy NFS. To FTP einai taxutero. To HTTP einai taxutero. Ta rcp kai ssh einai taxutera.

Akomh apofasismenoi na dokimasete; Ok.

Oi default parametroi toy NFS einai gia sxetika grhgores grammes, me mikro xrono anamonhs. An xrhsimopoihsete aytes tis default parametroys se arges grammes ychlhs anamonhs, 8a kanoyn to NFS na bgazei mhnumata la8wn sxetika me tis ergasies toy, na sas leei oti ta arxeia einai mikrotera ap' oso pragmatika einai, kai na kanei diafora alla mysthria pragmata.

To prwto pragma poy prepei na kanete, einai na mhn xrhsimopoihsete thn epilogh soft mount. Ayth 8a kanei ta timeouts na epistrefoyn kwdikes la8wn sto software, pragma poy pi8anotata den 8a einai ka8oloy kalos xeirismos ths katastashs. Aytos einai wraios tropos gia na kerdisete mysthriwdh kollhmata. anti8eta, xrhsimopoieiste thn hard mount option. Otan h hard einai energopoihmenh, ta timeouts prokaloun apeires prospa8eies epanaleitoyrgias, anti na parathsoyn o,ti prospa8ouse to software na kanei. Kai pragmatika, ayto einai ayto akribws poy 8elete.

To epomeno pragma poy prepei na kanete, einai na skalisete tis epiloges toy mount timeo kai retrans . Aytes perigrafontai sth man selida nfs(5), alla parte ki ena antigrafo edw :


       timeo=n        H timh se dekata toy deyteroleptoy, prin stalei 
                      h prwth epanekpomph meta apo ena RPC timeout. H 
                      default timh einai 7 dekata toy deyteroleptoy. 
                      Meta to prwto timeout, to timeout diplasiazetai 
                      diadoxika, mexris otoy ftasoyme s' ena megisto 
                      timeout twn 60 deyteroleptwn, h exoyn symbei arketes 
                      epanekpompes, wste na prokalesoyn ena meizon time-
                      out. Tote, an to filesystem  einai hard mounted, 
                      ka8e nea diadoxh timeouts janarxizei me diplasia 
                      arxikh timh ths prohgoumenhs seiras, kai jana 
                      diplasiazetai me ka8e epanekpomph. To megisto 
                      timeout einai panta 60 deyterolepta. Mporoume na 
                      epituxoyme kaluterh synolikh apodosh, ayjanontas 
                      to timeout s' ena diktyo me forto ergasias, s' enan 
                      argo server, h mesw pollwn routers h gateways. 

       retrans=n      O ari8mos twn mikrwn timeouts kai epanekpompwn poy 
                      prepei na symboun, prin emfanistei ena meizon 
                      timeout. H default timh einai 3 timeouts. Otan 
                      emfanistei ena meizon timeout, eite egkataleipetai 
                      h ergasia poy ginetai panw sto arxeio, h emfanizetai 
                      sthn konsola ena mhnyma "server not responding" 
                      (o server den apokrinetai). 

M' alla logia : An mia apanthsh den er8ei mesa ston xrono toy timeout twn 0.7 deyteroleptwn (700ms), o NFS client 8a epanalabei thn aithsh, kai 8a diplasiasei to timeout se 1.4 deyterolepta. Ean h apanthsh den fanei mesa se 1.4 deyterolepta, h aithsh 8a epanalhf8ei, kai to timeout 8a epanadiplasiastei sta 2.8 deyterolepta.

H taxuthta mias grammhs mporei na metrh8ei me ping enos paketoy me to idio mege8os me ta rsize/wsize.


$ ping -s 8192 lugulbanda
PING lugulbanda.uio.no (129.240.222.99): 8192 data bytes
8200 bytes from 129.240.222.99: icmp_seq=0 ttl=64 time=15.2 ms
8200 bytes from 129.240.222.99: icmp_seq=1 ttl=64 time=15.9 ms
8200 bytes from 129.240.222.99: icmp_seq=2 ttl=64 time=14.9 ms
8200 bytes from 129.240.222.99: icmp_seq=3 ttl=64 time=14.9 ms
8200 bytes from 129.240.222.99: icmp_seq=4 ttl=64 time=15.0 ms

--- lugulbanda.uio.no ping statistics ---
5 packets transmitted, 5 packets received, 0% packet loss
round-trip min/avg/max = 14.9/15.1/15.9 ms

Edw, o xronos anaferetai sto poso ekane to paketo toy ping, gia na paei mpros-pisw sto lugulbanda. (Ta 15ms einai arketa grhgora.) Se mia grammh 28 kbps mporeite na perimenete kati san 4000-5000ms, kai an h grammh einai fortwmenh, aytos o xronos 8a einai akomh megaluteros - polu eukola ftanei sth diplasia timh. Otan aytos o xronos einai megalos, tote leme oti yparxei "ychlh anamonh". Genika, gia megalutera paketa kai gia perissotero fortwmenes grammes, h anamonh ayjanetai. Ayjhste katallhla to timeo gia th grammh kai to fortio sas. Kai, mia poy h anamonh ayjanetai, otan xrhsimopoieite th grammh kai gia alles doyleies : An pote 8elhsete na xrhsimopoihsete ta FTP kai NFS taytoxrona, prepei na dokimasete na metrhsete toys xronoys ping enw xrhsimopoieite to FTP gia metafora arxeiwn, kai n' ayjhsete to timeo wste na tairiazei me thn anamonh ths grammhs sas.


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