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dCache on Steroids - Delegated Storage SolutionsTo cite this article: T Mkrtchyan et al 2017 J. Phys.: Conf. Ser. 898 062021

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This manuscript has been authored by Fermi Research Alliance, LLC under Contract No. DE-AC02-07CH11359 with the U.S. Department of Energy, Office of Science, Office of High Energy Physics.

C o nt e nt fr o m t his w or k m a y b e us e d u n d er t h e t er ms of t h e Cr e ati v e C o m m o ns Attri b uti o n 3. 0 li c e n c e . A n y f urt h er distri b uti o nof t his w or k m ust m ai nt ai n attri b uti o n t o t h e a ut h or(s) a n d t h e titl e of t h e w or k, j o ur n al cit ati o n a n d D OI.

P u blis h e d u n d er li c e n c e b y I O P P u blis hi n g Lt d 1

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d C a c h e o n St e r oi ds - D el e g at e d St o r a g e S ol uti o ns

T M k rt c h y a n 1 , F A d e y e mi1 , A As hi s h1 , G B e h r m a n n2 , P F u h r m a n n1 ,

D Lit vi nt s e v 3 , P Mill a r1 , A R ossi 3 , M S a h a k y a n1 a n d J St a r e k 1

1 D e ut s c h es El e ktr o n e n- S y n c hr otr o n D E S Y, H a m b ur g, G er m a n y2 N or di c e-I nfr astr u ct ur e C oll a b or ati o n ( N eI C), C o p e n h a g e n, D e n m ar k3 F er mi N ati o n al A c c el er at or L a b or at or y, B at a vi a, U S A

E- m ail: ti gr a n. m krt c h y a n @ d es y. d e

A bst r a ct

F or o v er a d e c a d e, d C a c h e. or g h as d eli v er e d a r o b ust s oft w ar e us e d at m or e t h a n 8 0U ni v ersiti es a n d r es e ar c h i nstit ut es ar o u n d t h e w orl d, all o wi n g t h es e sit es t o pr o vi d e r eli a bl est or a g e s er vi c es f or t h e W L C G e x p eri m e nts as w ell as m a n y ot h er s ci e ntifi c c o m m u niti es. T h efl e xi bl e ar c hit e ct ur e of d C a c h e all o ws r u n ni n g it i n a wi d e v ari et y of c o nfi g ur ati o ns a n dpl atf or ms - fr o m a S o C b as e d all-i n- o n e R as p b err y- Pi u p t o h u n dr e ds of n o d es i n a m ulti-p et a b yt e i nst all ati o n. D u e t o l a c k of m a n a g e d st or a g e at t h e ti m e, d C a c h e i m pl e m e nt e d d at apl a c e m e nt, r e pli c ati o n a n d d at a i nt e grit y dir e ctl y. T o d a y, m a n y alt er n ati v es ar e a v ail a bl e: S 3,Gl ust er F S, C E P H a n d ot h ers. W hil e s u c h s ol uti o ns p ositi o n t h e ms el v es as s c al a bl e st or a g es yst e ms, t h e y c a n n ot b e us e d b y m a n y s ci e ntifi c c o m m u niti es o ut of t h e b o x. T h e a bs e n c e ofc o m m u nit y- a c c e pt e d a ut h e nti c ati o n a n d a ut h ori z ati o n m e c h a nis ms, t h e us e of pr o d u ct s p e cifi cpr ot o c ols a n d t h e l a c k of n a m es p a c e ar e s o m e of t h e r e as o ns t h at pr e v e nt wi d e-s c al e a d o pti o nof t h es e alt er n ati v es. M ost of t h es e li mit ati o ns ar e alr e a d y s ol v e d b y d C a c h e. B y d el e g ati n gl o w-l e v el st or a g e m a n a g e m e nt f u n cti o n alit y t o t h e a b o v e- m e nti o n e d n e w s yst e ms a n dpr o vi di n g t h e missi n g l a y er t hr o u g h d C a c h e, w e pr o vi d e a s ol uti o n w hi c h c o m bi n es t h eb e n efits of b ot h w orl ds - i n d ustr y st a n d ar d st or a g e b uil di n g bl o c ks wit h t h e a c c ess pr ot o c olsa n d a ut h e nti c ati o n r e q uir e d b y s ci e ntifi c c o m m u niti es. I n t his p a p er, w e f o c us o n C E P H, ap o p ul ar s oft w ar e f or cl ust er e d st or a g e t h at s u p p orts fil e, bl o c k a n d o bj e ct i nt erf a c es. C E P H isoft e n us e d i n m o d er n c o m p uti n g c e nt ers, f or e x a m pl e as a b a c k e n d t o O p e n St a c k s er vi c es. W ewill s h o w pr ot ot y p es of d C a c h e r u n ni n g wit h a C E P H b a c k e n d a n d dis c uss t h e b e n efits a n dli mit ati o ns of s u c h a n a p pr o a c h. W e will als o o utli n e t h e r o a d m a p f or s u p p orti n g ‘ d el e g at e dst or a g e’ wit hi n t h e d C a c h e r el e as es.

1. I nt r o d u cti o n

d C a c h e[ 1][ 2] is a s oft w ar e s ol uti o n t h at pr o vi d es a hi g hl y s c al a bl e, di stri b ut e d st or a g e s yst e m wit h asi n gl e-r o ot e d n a m es p a c e b y c o m bi ni n g a n u m b er of i n di vi d u al n o d es. B y a d di n g m or e st or a g e n o d es,t h e t ot al c a p a cit y a n d t hr o u g h p ut ar e i n cr e as e d si m ult a n e o usl y. d C a c h e h as s e v er al m e c h a ni s m s f ord at a pl a c e m e nt a n d pr ot e cti o n: fil e r e pli c ati o n f or r e d u n d a n c y, h o p pi n g m a n a g er t o mi gr at e d at a fr o mW A N ‘i n p ut b uff ers’ t o L A N ‘l o c al s er v ers’, i n or d er t o s e p ar at e i n c o mi n g str e a mi n g d at a fr o mr a n d o m a c c ess fr o m t h e l o c al a n al ysi s f ar m s, f or e x a m pl e, p o ol-t o- p o ol r e pli c ati o n o n l o a d, i n or d er t ooffl o a d tr a nsf ers fr o m h ot d at a s er v ers a n d v ari o us mi gr ati o n t as ks, t o a dj ust d at a pl a c e m e nt ore v a c u at e/r etir e o n e of t h e d at a s er v ers. I n a d diti o n t o st or a g e m a n a g e m e nt, d C a c h e s u p p ort s m ulti pl ea c c ess pr ot o c ol s f or st ori n g a n d r etri e vi n g d at a: D C A P, Gri d F T P, H T T P, N F S, W e b D A V a n d Xr o ot D.I n d ustr y st a n d ar d as w ell as H E P-s p e cifi c a ut h e nti c ati o n a n d a ut h ori z ati o n m e c h a nis m s ar e pr o vi d e d:K er b er os, O p e nI D- C o n n e ct, Us er n a m e + P ass w or d, X 5 0 9.

T his m a n us cri pt h as b e e n a ut h or e d b y F er mi R es e ar c h Alli a n c e, L L C u n d er C o ntr a ct N o. D E- A C 0 2- 0 7 C H 1 1 3 5 9 wit h t h e U. S. D e p art m e nt of E n er g y, Offi c e of S ci e n c e, Offi c e of Hi g h E n er g y P h ysi cs.

F E R MI L A B- C O N F- 1 7- 6 4 7- C DA C C E P T E D

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As d es cri b e d a b o v e, d C a c h e f u n cti o n alit y c a n b e s plit i nt o t hr e e c at e g ori es: A g gr e g ati n g m ulti pl e st or a g e n o d es i nt o a si n gl e r o ot e d distri b ut e d st or a g e s yst e m. Pr o vi di n g a c c ess t o t h e st or a g e s yst e m vi a v ari o us a c c ess pr ot o c ols a n d s e c urit y m e c h a nis m s. M a n a gi n g d at a pl a c e m e nt, r e pli c ati o n a n d r eli a bilit y.

2. M oti v ati o n

F or d e c a d es, h ar d w ar e/ s oft w ar e R AI D- b as e d[ 3] s yst e ms w er e us e d b y d C a c h e as st or a g e n o d es. Wit ht h e gr o wi n g si z e of a si n gl e h ar d di s k as w ell as t h e n u m b er of di s ks i n a si n gl e b o x, t his a p pr o a c hd o es n ot s c al e a n y m or e. A s i n gl e di s k f ail ur e r e q uir es i m m e di at e a cti o n t o r e pl a c e t h e f ail e d dis k.T his a d ds a n o p er ati o n al o v er h e a d a n d i n cr e as es t h e t ot al c ost of o w n ers hi p ( T C O). M or e o v er, t h el o n g R AI D r e b uil d ti m es, – a b o ut 1 T B p er h o ur, – d e cr e as e o v er all n o d e p erf or m a n c e a n d r e d u c e e n d-us er e x p eri e n c e.

A st or a g e n o d e, w hi c h i s t ol er a nt t o m ulti pl e di s k f ail ur es wit h a l o w o p er ati o n al o v er h e a d, i sr e q uir e d t o pr o vi d e a r eli a bl e s er vi c e.

3. C E P H

T h er e ar e m ulti pl e di stri b ut e d st or a g e s yst e m s a v ail a bl e t o d a y. U nf ort u n at el y, t h e y c a n n ot f ulfill allt h e r e q uir e m e nt s of s ci e ntifi c c o m m u niti es - eit h er d u e t o t h e l a c k or i n c o m p ati bilit y of t h e us u ala ut h e nti c ati o n m e c h a nis m s or s p e cifi c a c c ess pr ot o c ol s. N e v ert h el ess, b y c o m bi ni n g s u c h s yst e mswit h d C a c h e w e c a n pr o vi d e t h e us u al f u n cti o n alit y a n d still b e n efit fr o m f u n cti o n alit y pr o vi d e d b ys yst e m s li k e C E P H[ 4].

C E P H is a n o p e n-s o ur c e st or a g e pl atf or m w hi c h i m pl e m e nts a si n gl e distri b ut e d o bj e ct st or e.It o p er at es wit h o ut a si n gl e p oi nt of f ail ur e a n d is s c al a bl e t o t h e e x a b yt e l e v el. D at a pr ot e cti o n i sa c hi e v e d b y r e pli c ati o n a n d er as ur e c o di n g. As a r es ult of it s d esi g n, t h e s yst e m i s b ot h s elf- h e ali n ga n d s elf- m a n a gi n g, mi ni mi zi n g a d mi ni str ati o n ti m e a n d ot h er c osts.

B e c a us e of it s c a p a biliti es, C E P H is oft e n us e d as a b a c k e n d st or a g e f or O p e n St a c ki nst all ati o ns a n d i s alr e a d y d e pl o y e d at a n u m b er of sit es, w hi c h m a k es it attr a cti v e as a b a c k e n d f ord C a c h e as w ell.

I n C E P H, a mi ni m al st or a g e u nit c all e d O S D – o bj e ct st or a g e d e vi c e, – i s t y pi c all y a si n gl edi s k. O n e or m or e O S Ds ar e gr o u p e d i nt o s o- c all e d pl a c e m e nt gr o u ps ( P G). St or a g e of a n o bj e ct i n apl a c e m e nt gr o u p tri g g ers t h e cr e ati o n of t h e r e q uir e d n u m b er of r e pli c as o n o n e or m or e O S Ds. Avirt u al c o nt ai n er, or p o ol, c o nsi st s of o n e or m or e pl a c e m e nt gr o u ps ( Fi g ur e 1). T h e r e pli c ati o n f a ct ora n d/ or er as ur e c o di n g r ul es ar e att a c h e d t o t h e p o ol. T h e “ C o ntr oll e d R e pli c ati o n U n d er S c al a bl eH as hi n g ” al g orit h m, or C R U S H[ 5], is us e d f or s el e cti n g a n a p pr o pri at e pl a c e m e nt gr o u p w h e ncr e ati n g or a c c essi n g a n o bj e ct.

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3

Fi g u r e 1. C E P H d at a or g a ni z ati o n i nt er n al str u ct ur e

4. d C a c h e - C E P H i nt e g r ati o n

C E P H pr o vi d es o bj e ct-, bl o c k-, a n d fil e i nt erf a c es. T h e o bj e ct i nt erf a c e pr o vi d es b asi c P U T, G E T a n dD E L E T E o p er ati o ns. W hil e st ori n g d at a i n C E P H as o bj e ct s is a c o m m o n pr a cti c e, it d o es n ot c o m ewit h o ut its li mit ati o ns. S p e cifi c all y, t h e o bj e ct i nt erf a c e s is l ess s uit a bl e f or i nt e gr ati o n wit h d C a c h eb e c a us e t h e o bj e ct s ar e st or e d o n a si n gl e O S D, m a ki n g it i m p ossi bl e t o writ e t h e m usi n g r a n d o ma c c ess, w hi c h is r e q uir e d b y t h e d c a p, nfs a n d xr o ot d pr ot o c ols. O n t h e ot h er h a n d, t h e bl o c k i nt erf a c eall o ws r a n d o m a c c ess o n s o- c all e d r a d os bl o c k d e vi c es ( R B D). M or e o v er, R B D s u p p orts stri pi n g o v erm ulti pl e O S Ds a n d pr o vi d es r e a d-t hr o u g h/ writ e- b a c k c a c hi n g o ut of t h e b o x, w hi c h m a k es t h e bl o c ki nt erf a c e v er y attr a cti v e f or d C a c h e i nt e gr ati o n. F or e v er y fil e st or e d i n t h e d C a c h e a n e w R B D i m a g eis cr e at e d. N ot e, h o w e v er, t h at t hi s is n ot a c o m m o nl y us e d pr a cti c e f or C E P H; h e n c e l ar g e s c al ep erf or m a n c e st u di es ar e r e q uir e d.

I n d C a c h e, t h e c o m p o n e nt w hi c h st or es d at a i s als o c all e d a p o ol ( w hi c h m a y cr e at e c o nf usi o ni n t h e C E P H c o nt e xt). All p o ol s o p er at e i n d e p e n d e ntl y fr o m e a c h ot h er a n d m a k e t h eir o w n d e ci si o nsw h e n t o fl us h fil es t o t a p e, w h e n t o r e m o v e c a c h e d c o pi es a n d w h e n t o d estr o y t h e r e m o v e d fil es. A nis ol at e d d esi g n of t hi s s ort m a k es it v er y e as y t o s c al e u p d C a c h e i nst a n c es t o t h o us a n ds of p o ol swit h o ut p erf or m a n c e d e gr a d ati o n c a us e d b y i nt er- c o m m u ni c ati o n o v er h e a d. A p o ol’s r e p osit or y h ast w o m ai n f u n cti o ns: tr a c ki n g t h e st at e of t h e st or e d fil es, – s u c h as b ei n g r e c ei v e d fr o m cli e nt, b ei n gr e c ei v e d fr o m st or e, or n e e di n g t o b e fl us h e d t o t a p e, – a n d pr o vi di n g I O a c c ess t o t h e d at a. I n a d diti o nt o tr a c ki n g fil e st at es, t h e p o ol st or es a s u bs et of m et a d at a ass o ci at e d wit h a fil e, s u c h as fil e si z e,a c c ess l at e n c y a n d r et e nti o n p oli c y.

Fi g u r e 2. d C a c h e i nt e gr ati o n wit h C E P H

T h e d C a c h e p o ol cl e arl y s e p ar at es t h e m et a d at a a n d d at a I O p at hs o n t h e b a c k e n d st or a g e. T h em et a d at a is st or e d s e p ar at el y fr o m t h e d at a fil es dir e ct or y, i n t h e f or m of a B er k el e y- D B or a s et offil es. T h e d at a a c c ess is d o n e vi a a p osi x i nt erf a c e t o t h e u n d erl yi n g fil e s yst e m. E v e n w h e n d C a c h ep o ol us es C E P H as a b a c k e n d, it is still ass o ci at e d wit h a si n gl e C E P H p o ol. T h e m et a d at a a c c ess

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4

r e m ai ns u n c h a n g e d, b ut a n y I O o p er ati o ns ar e s e nt dir e ctl y t o C E P H vi a li br a d os. T hi s a p pr o a c h k e e psot h er p o ol c o m p o n e nt s u n a w ar e of C E P H b a c k e n d, w hil e pr es er vi n g t h e p o ol’s f ull f u n cti o n alit y,i n cl u di n g mi gr ati o n, p 2 p a n d H S M c o n n e cti vit y ( Fi g ur e 2).

5. H S M c o n n e cti vit y

T o fl us h or r est or e a fil e t o/fr o m H S M, d C a c h e us es a n e xt er n al s cri pt. U p o n fl us hi n g t hi s s cri pt t a k es

t h e l o c al p at h of t h e fil e t o b e fl us h e d a n d r et ur ns a n H S M-s p e cifi c U RI, w hi c h i s st or e d b y d C a c h e.U p o n r est or e, t h e s cri pt t a k es t h e pr e vi o usl y st or e d U RI a n d t h e l o c al p at h t o w h er e t h e fil e s h o ul d b er est or e d:

hs m. s h p ut /l o c al/ p at h/t o/fil e

orhs m. s h g et - uri < uri > /l o c al/ p at h/t o/fil e

W h e n t h e p o ol us es C E P H as a b a c k e n d, t h e n a C E P H-s p e cifi c U RI is us e d i nst e a d of t h e l o c al p at h:

c e p h- hs m. s h g et - uri < uri > r b d:// < c e p h _ p o ol >/ <fil e _i d >

T h e fil e _i d c orr es p o n ds t o t h e fil e’s u ni q u e i d e ntifi er wit hi n d C a c h e, c all e d t h e p nf si d .

6. C u r r e nt st at us

St arti n g fr o m d C a c h e v ersi o n 3. 0. 0, a si n gl e c o nfi g ur ati o n o pti o n c a n b e us e d t o l e v er a g e C E P H as ab a c k e n d f or t h e p o ol s:

p o ol. b a c k e n d = c e p h

A d diti o n all y, t h e l o c ati o n of c e p h. c o nf a n d t h e cl ust er n a m e c a n b e c o nfi g ur e d.

As wit h a n y ot h er f u n cti o n alit y i n d C a c h e, C E P H s u p p ort p ass e d all o ur t esti n g. H o w e v er, si n c e n o n eof t h e c oll a b or ati n g sit es s u c h as D E S Y, F er mi L a b a n d N D G F, ar e usi n g it i n pr o d u cti o n, a n i nt e nsi v epr e- pr o d u cti o n t esti n g b y sit es i s ess e nti al.

7. P e rf o r m a n c e e v al u ati o n

T h e d e v el o p m e nt pr o c ess w as c o n c e ntr at e d o n st a bilit y, f u n cti o n al f e at ur e s et a n d i nt er o p er a bilit y ofC E P H a n d P O SI X b as e d p o ols. A d diti o n all y, a n y p erf or m a n c e e v al u ati o n r e q uir e d e e p k n o wl e d g e a n dpr o d u cti o n e x p eri e n c e of C E P H. T hi s h ar d t as k w e l e a v e t o sit e a d mi ns w h o w as w aiti n g f or d C a c h e-C E P H i nt e gr ati o n.

8. F ut u r e pl a ns

As m e nti o n e d e arli er, w h e n usi n g C E P H as a b a c k e n d, e a c h d C a c h e p o ol is ass o ci at e d wit h a si n gl eC E P H p o ol. W hil e t his n at ur all y fit s wit h t h e c urr e nt d C a c h e d esi g n, it li mits t h e f u n cti o n alit y w hi c hC E P H or a n y ot h er s h ar e d b a c k e n d c a n pr o vi d e. As a n y n o d e i n t h e C E P H cl ust er c a n a c c ess a n y

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5

C E P H p o ol, a n e w p ar a di g m c a n b e cr e at e d w h er e a si n gl e C E P H p o ol c a n b e s er v e d b y m ulti pl ed C a c h e p o ol s. T hi s t ur ns d C a c h e p o ol s i nt o a t hi n l a y er, a cti n g as a st at el ess g at e w a y b et w e e n t h en a m es p a c e, t h e v ari o us pr ot o c ol s a n d t h e b a c k e n d st or a g e. T h e y c a n b e d y n a mi c all y st art e d a n dst o p p e d as m or e b a n d wi dt h i s r e q uir e d.

It m a k es s e ns e t o p us h r e pli c ati o n a n d d at a mi gr ati o n d o w n i nt o t h e u n d erl yi n g st or a g es yst e m. H o w e v er, wit h t h e gr o wi n g d e m a n d f or di stri b ut e d i nst all ati o ns, w e c a n n ot ass u m e t h at alld C a c h e p o ols will b e r u n ni n g o n t o p of C E P H wit hi n a si n gl e i nst a n c e. As a r es ult, s o m e i nst all ati o nswill c o nt ai n b ot h C E P H- b as e d a n d r e g ul ar R AI D- b as e d ar e as. S u c h d e pl o y m e nt s still m ust b e a bl e t om o v e d at a b et w e e n diff er e nt p o ol s, i n d e p e n d e nt of t h eir b a c k e n d t y p e ( Fi g ur e 3).

Fi g u r e 3. C E P H a n d r e g ul ar p o ol c o e xi sts i n t h e s a m e d e pl o y m e nt

9. S u m m a r y

D u e t o o p er ati o n al o v er h e a d, tr a diti o n al R AI D- b as e d s yst e m s b e c o m e l ess s uit a bl e as b uil di n g bl o c ksf or l ar g e-s c al e st or a g e s yst e m s. N o w a d a ys t h er e ar e pl e nt y of alt er n ati v e t e c h n ol o gi es a v ail a bl e w hi c hai m t o pr o vi d e ri c h er f u n cti o n alit y a n d fl e xi bilit y wit h o ut c o m pr o misi n g st a bilit y. Eff e cti v e v ersi o n3. 0. 0, d C a c h e c a n us e C E P H as a b a c k e n d f or d at a st or a g e a n d still pr o vi d e a f ull r a n g e off u n cti o n alit y i n cl u di n g r e pli c ati o n, mi gr ati o n a n d H S M c o n n e cti vit y. B as e d o n pr o d u cti o n e x p eri e n c e,m or e of t h e n ati v e C E P H f u n cti o n alit y will b e dir e ctl y us e d b y d C a c h e. N e v ert h el ess, d C a c h e willc o nti n u e t o s u p p ort tr a diti o n al R AI D- b as e d s yst e m s a n d e v e n s u p p ort mi x e d e n vir o n m e nt s, w h er eC E P H- a n d R AI D- b a c k e d p o ols c a n b e mi x e d i n a si n gl e i nst all ati o n.

R ef er e n c es[ 1] w w w. d c a c h e. or g[ 2] d C a c h e,t h e O v er vi e w htt ps:// w w w. d c a c h e. or g/ m a n u al s/ d c a c h e- w hit e p a p er-li g ht. p df[ 3] R e d u n d a nt Arr a y of I n d e p e n d e nt Di s ks htt ps:// e n. wi ki p e di a. or g/ wi ki/ R AI D[ 4] w w w. c e p h. c o m[ 5] T h e C R U S H al g orit h m htt p:// d o cs. c e p h. c o m/ d o cs/ m ast er/r a d os/ o p er ati o ns/ cr us h- m a p/