[Linuxtrent] Qual'è il miglior valore per "Stripe size" in un raid6 ?

  • From: Marco Agostini <comunelevico@xxxxxxxxx>
  • To: linuxtrent@xxxxxxxxxxxxx
  • Date: Thu, 19 Nov 2009 16:54:06 +0100

Ciao, riporto una parte del testo dal link
http://wiki.tldp.org/LVM-on-RAID proposto in un precedente post da

Chunks and Stripes

For most RAID levels in use today data is split in to building blocks
called chunks . A typical chunk size is 64kb; but usually it must be
comprised of a power of two (1, 2, 4, 8 etc) and a multiple of the
block device's block size.

A stripe is composed of one chunk per device; the size of a stripe is
thus always a multiple of the chunk size.

For raid 1, there is no striping, since each device contains a full
copy. For all other levels of modern day RAID stripes are used.

Performance considerations are a factor when striping. Even on devices
without parity, large writes are most efficient when distributed
nearly evenly across all the data drives. Reads are even more
effective when using multiple drives. Using multiple devices yields
higher sustained and higher burst read rates. A smaller stripe size
may make more sense for applications that are trying to put a small
number of records on each device.

Performance should be viewed the most critical and from the most
common cases. Larger chunk sizes, to a point, increase performance on
large writes, such as archives, videos, even large graphics or
compressed audio files. My gut feeling on the matter is that a
reasonable chunk size, like the default of 64KB that mdadm currently
uses, combined with a flush every few seconds policy would be good
enough for most applications.

Questo è il mio caso specifico:
- stò configurando un raid 6 (hardware) con 5 dischi su di un nuovo
server, mi viene proposto come valore di default per stripe 256KB.
- sul server verrà installato proxmox per gestire la
virtualizzazione.... di conseguenza rifacendomi al testo sopra dovrei
impostare un "Larger chunk sizes, to a point, increase performance on
large writes" visto che ho a che fare con file voluminosi (quelli
delle macchine virtuali).
- i valori possibili sono 16KB, 32KB, 64KB, 128KB, 256KB, 512KB, 1024KB
- sul server è attiva anche una cache con batteria a tampone per il
controller raid.

.... qualcuno di voi ha già sperimentato ?

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