beurk, quelqu'un qui conseil de faire plein de partition pour gérer
du mail n'est pas vraiment à écouter. C'est un admin qui se fait
chier & qu'aime bien se provoquer des problème.
Le concat, en plus des problèmes évoqués par alex pose un autre
problème : le premier disque se tape la table des inodes & va très
vite se retrouver saturé. À coté de ça, les bouts d'optimisations
qu'il me semble pas vraiment convaincantes. Même s'il a raison (ce
que je ne crois pas), il y a toujours l'option de définir une taille
de strip proche de la taille moyenne d'une bal pour contredire son
explication.
Le 12 juil. 05 à 13:16, Gerard Henry a écrit :
bonjour,
y a t il une difference entre le stripe et le concat?
en relisant un vieux fil de discussion, qqun disait qu'il valait
mieux concatener que stripper:
Comme je suis pas sur d'avoir tout compris, je mets ici une partie
du mail en copie
"It would seem with 12,000 users accessing mailboxes via POP and
similar,
and with a steady stream of incoming messages, what you'd really want
would be good random-access performance. Striping is going to give you
good sequential performance for one-request-at-a-time kind of loads,
which is not what you have.
Also, there is a cost to striping: when joeuser logs in via POP
(or IMAP or whatever), he'll typically download his whole mailbox.
Unless he has a very fast network connection, this will not happen
in one burst but will be a few I/O requests scattered over the
course of a few seconds (or sometimes minutes). If you use
striping, his mailbox is likely to be close to contiguous
and will thus span multiple spindles in the stripe. So, it would
seem that every time he needs to download his 250k mailbox, if you
have 5 disks in the stripe, every single disk head will have to
move to the same general area, where his mailbox is. This seems
kind of silly to me. Fetching his data as fast as possible
isn't what's desired; what you need is the ability to fetch his
data with minimal impairment to your ability to fetch others'
data at the same time.
Imagine you concatenate instead. Then, most likely (although
not definitely), joeuser's mailbox lies all on one disk.
If you have 5 concatenated disks, maybe you can get lucky and
have 5 people logged in at once, with each one fetching stuff
from their mailbox off one spindle and not disturbing others.
In fact, were it not for the extra administration headache,
I'd be really tempted to suggest making a separate filesystem
for each disk and splitting up /var/spool/mail so that different
users' mailboxes are hashed onto different disks.
So, it seems to me that perhaps a good compromise would be to
create a series of two-way mirrors and then concatenate the
mirrors. This would allow joeuser's mailbox activity to affect
only one spindle, and every mailbox would be accessible through
one of two spindles, whichever is most convenient."
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