"With 20 disk of 4TB you have a total capacity of 80TB. If you run all of them as RAID6 then you have a total of 72TB."
And that's the point! I'm trying to understand if I can create more RAID6 arrays and how my controller handles disk failures in that case. First I think we need to clarify terminology related to Megaraid Storage Manager and for this reason I attach here a screenshot -> (phyical drives -> http://pasteboard.co/NC3O60x.png and logical drives -> http://pasteboard.co/NC8DLcM.png ) So, reading this -> http://www.cisco.com/c/dam/en/us/td/docs/unified_computing/ucs/3rd-party/lsi/mrsas/userguide/LSI_MR_SAS_SW_UG.pdf (page 41) I think I have a RAID (6 in my case) array as a drive group and a volume as a Virtual Drive. If this is right, I should discover how much RAID array my controller supports. Actually I have 20 disks, but I can add more. However, reducing rebuild array time is my goal, so I think that create a virtual drive for each drive group is the right way. Please give me some advises.... Thanks 2015-09-18 13:02 GMT+02:00 Kai Dupke <kdu...@suse.com>: > On 09/18/2015 09:28 AM, Marco Marino wrote: > > Can you explain me this? 16 volumes? > > > With 20 disk of 4TB you have a total capacity of 80TB. If you run all of > them as RAID6 then you have a total of 72TB. > > If you ask your controller to create a 8TB volume, this volume is spread > across all the 20 disk. As 2 stripes are used for parity, you have > 20-2=18 data stripes per volume. This makes each stripe 444G big, > leaving 3500G free for other volumes. > > If you fill up the remaining 3500G with volumes the same way, you get 8 > additional volumes (OK, the last volume is <8TB then). > > In total you have 9 volumes then, each disk has data/parity on all of > these volumes. > > 9x8=72, voila! > > If a disk error appear and the controller marks the disk dead then all 9 > volumes are affected. > > With 20 6TB/8TB drives, you just get more 8TB volumes using this way. > > What would of course reduce the risk is to always use <20 disk in one > raid6 volume, so not each disk serves all volumes. > > Another issue is about performance, not every RAID controller performs > best with 20 drives. Adaptec recommends an odd number of drives, with 7 > or 9 drives performs best AFAIK. > > So you could make volume 1 on disks 1-9, volume 2 on disk 2-10, volume 3 > on disk 3-11 etc. etc. > > Or consider using some combination of RAID6 and RAID1, but this gives > you way less available disk size (and no, I have no calculation handy on > the chance for failure for RAID6 vs. RAID15 vs. RAID16) > > greetings kai > > > > > > Thank you > > > > > > > > 2015-09-17 15:54 GMT+02:00 Kai Dupke <kdu...@suse.com>: > > > >> On 09/17/2015 09:44 AM, Marco Marino wrote: > >>> Hi, I have 2 servers supermicro lsi 2108 with many disks (80TB) and I'm > >>> trying to build a SAN with drbd and pacemaker. I'm studying, but I have > >> no > >>> experience on large array of disks with drbd and pacemaker, so I have > >> some > >>> questions: > >>> > >>> I'm using MegaRAID Storage Manager to create virtual drives. Each > virtual > >>> drive is a device on linux (eg /dev/sdb, /dev/sdc.....), so my first > >>> question is: it's a good idea to create virtual drive of 8 TB (max)? > I'm > >>> thinking to rebuild array time in case of disk failure (about 1 day > for 8 > >> > >> It depends on your disks and RAID level. If one disk fails the content > >> of this disk has to be recreated by either copying (all RAID levels with > >> some RAID 1 included) or calculating (all with no RAID1 included), in > >> the later case all disks get really stressed. > >> > >> If you run 20x4TB disks as RAID6, then an 8TB volume is only ~500G per > >> disk. However, if one disk fails, then all the other 15 volumes this > >> disk handles are broken, too. (BTW, most raid controller can handle > >> multiple stripes per disk, but usually only a handful) In such case the > >> complete 4TB of the broken disk has to be recovered, affecting all 16 > >> volumes. > >> > >> On the other side, if you use 4x5x4TB as 4x 12TB RAID6, a broken disk > >> only affects one of 4 volumes - but at the cost of more disks needed. > >> > >> You can do the similar calculation based on RAID16/15. > >> > >> The only reason I see to create small slices is to make them fit on > >> smaller replacement disks, which might be more easily available/payable > >> at time of error (but now we are entering a more low cost area where > >> usually SAN and DRBD do not take place). > >> > >> greetings > >> Kai Dupke > >> Senior Product Manager > >> Server Product Line > >> -- > >> Sell not virtue to purchase wealth, nor liberty to purchase power. > >> Phone: +49-(0)5102-9310828 Mail: kdu...@suse.com > >> Mobile: +49-(0)173-5876766 WWW: www.suse.com > >> > >> SUSE Linux GmbH - Maxfeldstr. 5 - 90409 Nuernberg (Germany) > >> GF:Felix Imendörffer,Jane Smithard,Graham Norton,HRB 21284 (AG Nürnberg) > >> > >> _______________________________________________ > >> Users mailing list: Users@clusterlabs.org > >> http://clusterlabs.org/mailman/listinfo/users > >> > >> Project Home: http://www.clusterlabs.org > >> Getting started: > http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf > >> Bugs: http://bugs.clusterlabs.org > >> > > > > > > > > _______________________________________________ > > Users mailing list: Users@clusterlabs.org > > http://clusterlabs.org/mailman/listinfo/users > > > > Project Home: http://www.clusterlabs.org > > Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf > > Bugs: http://bugs.clusterlabs.org > > > > > > Kai Dupke > Senior Product Manager > Server Product Line > -- > Sell not virtue to purchase wealth, nor liberty to purchase power. > Phone: +49-(0)5102-9310828 Mail: kdu...@suse.com > Mobile: +49-(0)173-5876766 WWW: www.suse.com > > SUSE Linux GmbH - Maxfeldstr. 5 - 90409 Nuernberg (Germany) > GF:Felix Imendörffer,Jane Smithard,Graham Norton,HRB 21284 (AG Nürnberg) > > _______________________________________________ > Users mailing list: Users@clusterlabs.org > http://clusterlabs.org/mailman/listinfo/users > > Project Home: http://www.clusterlabs.org > Getting started: http://www.clusterlabs.org/doc/Cluster_from_Scratch.pdf > Bugs: http://bugs.clusterlabs.org >
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