Re: RAID Performance Questions
Milo Hyson wrote:
> I also ran some performance tests with a stock build of PostgreSQL 8.0
> to get a different angle on things. Two tests were run on each of the
> UDMA system drive, the RAID 5 unit, and the RAID 10 unit. The first
> tested sequential-scans through a 58,000+ record table. The second
> tested random index-scans of the same table. These were read-only tests
> -- no write tests were performed. The results are as follows:
>
> Unit Seq/secIndex/sec
> --
> single 0.550 2048.983
> raid5 0.533 2063.900
> raid10 0.533 2093.283
58,000 records is WAY too small for any benefits to come out, unless the
records are very large ("wide"). The database and the OS will cache as
much data they can - with such a small number of records it's very
probable they will all be cached and the drives won't get any IO (and
it's lucky for you that it works this way). You can verify this
hypothesis with iostat and similar utilities.
This is also something you'll need to consider: unless you have more
data than fits in your memory, don't bother with the drives. When your
data DOES grow enough that it doesn't fit in memory (or actually - not
all of it, just the mostly accessed bits), you'll take a dramatic
performance hit which you can fix only with a large numbers of drives
(as other said - no less than 5 fast drives to get any kind of decent
performance). In that case, it's way cheaper and faster to add as much
memory as the motherboard can handle before even touching the drives.
(the above explanation holds for read-mostly loads. for write intensive
loads, go immediately to the 5+ drives option and try to avoid RAID5).
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Re: RAID Performance Questions
On Jan 25, 2007, at 13:50, Jeff Mohler wrote: How about one large raid, and two partitions to serve each purpose? Being so limited in HW, youre either going to take a _huge_ performance hit with only 2 disks per raid (unless Raid0), or an availability hit with everything on one RAID set. I suppose availability is more important than performance. However reliability is even more important. My big concern with a single, large array is that should the array become corrupted for any reason, I'll lose both the live and the backup. Also, in that configuration, the backup becomes little more than transparent revision control. Another factor to consider (which I should have mentioned earlier) is that with the exception of any locally hosted databases, this is a NAS box. All data access will be via FastEthernet, and that's more of a bottleneck than any disks I have. -- Milo Hyson CyberLife Labs ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: RAID Performance Questions
How about one large raid, and two partitions to serve each purpose? Being so limited in HW, youre either going to take a _huge_ performance hit with only 2 disks per raid (unless Raid0), or an availability hit with everything on one RAID set. But..considering the costs of adding RAID to a server..take a peek here for a high(er) perfomance RAID solution..if Fbsd had an iscsi layer like linux has had for...5yrs or so..this would be a slam dunk as you can still serve it as block data. If that cant help you, it might help the next guy with only a few K's to spend on large disks and raid controllers. On 1/25/07, Milo Hyson <[EMAIL PROTECTED]> wrote: On Jan 25, 2007, at 12:15, Chuck Swiger wrote: > Still, you also ought to consider that a 3-disk RAID-5 > configuration is very much not ideal from either an efficiency or > performance standpoint-- you want more like 5 or 6 drives being > used, in which case your performance numbers ought to increase > some. This is also somewhat true of the 4-disk RAID-10 config; > using 6 or all 8 drives would likely improve performance compared > with striping against only two disks. Unfortunately, I'm a bit limited in terms of equipment and application requirements. For starters, the app specs currently call for two arrays: one for general file-serving and databases, and the other for backups. Due to limited hardware I'm to run both on the same controller. Far from ideal, I know, but it's what I have. Second, I need to keep at least one drive as a hot-spare. Thus, I have seven drives that I somehow need to partition into two groups and maximize performance without sacrificing reliability. Lastly, the RAID controller does not permit more than two drives in a RAID-1 set. Any suggestions? -- Milo Hyson CyberLife Labs ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]" ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: RAID Performance Questions
On Jan 25, 2007, at 12:15, Chuck Swiger wrote: Still, you also ought to consider that a 3-disk RAID-5 configuration is very much not ideal from either an efficiency or performance standpoint-- you want more like 5 or 6 drives being used, in which case your performance numbers ought to increase some. This is also somewhat true of the 4-disk RAID-10 config; using 6 or all 8 drives would likely improve performance compared with striping against only two disks. Unfortunately, I'm a bit limited in terms of equipment and application requirements. For starters, the app specs currently call for two arrays: one for general file-serving and databases, and the other for backups. Due to limited hardware I'm to run both on the same controller. Far from ideal, I know, but it's what I have. Second, I need to keep at least one drive as a hot-spare. Thus, I have seven drives that I somehow need to partition into two groups and maximize performance without sacrificing reliability. Lastly, the RAID controller does not permit more than two drives in a RAID-1 set. Any suggestions? -- Milo Hyson CyberLife Labs ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: RAID Performance Questions
On Jan 25, 2007, at 10:50 AM, Milo Hyson wrote: The write times of both RAID configurations are slower than the single drive (which is expected due to having to write to multiple drives). However, I wasn't expecting such a drastic reduction (about 50%). The read times, although faster, are only marginally so in per-char transfer. They're a bit better in block performance, but still not what I would expect. It would seem to me that a read spread across four drives should see more than a 45% performance increase. The highest rate recorded here is only a quarter of the PCI bus-speed, so I doubt that's a bottleneck. CPU load peaks at 50%, so I don't see that being a problem either. Single-byte accesses are a worst-case scenario for RAID throughput; the block rates are generally more applicable to the performance you'll see for decently-written applications and many use-case scenarios. If you've got a UPS or battery-backup option for the RAID card enabled, consider turning on write-back mode rather than write- thru mode, which ought to improve write performance pretty significantly. Still, you also ought to consider that a 3-disk RAID-5 configuration is very much not ideal from either an efficiency or performance standpoint-- you want more like 5 or 6 drives being used, in which case your performance numbers ought to increase some. This is also somewhat true of the 4-disk RAID-10 config; using 6 or all 8 drives would likely improve performance compared with striping against only two disks. I also ran some performance tests with a stock build of PostgreSQL 8.0 to get a different angle on things. [ ... ] Any performance benefit of RAID in these tests is almost nonexistent. Am I doing something wrong? Am I expecting too much? Any advice that can be offered in this area would be much appreciated. Most databases dislike any form of RAID except plain old RAID-1 mirroring, but absolutely hate RAID-5. Databases can do OK with big RAID-10 combinations, too, but ask any experienced DBA what they'd like, and they'd rather have as many RAID-1 spindles available as possible compared with any other drive arrangement. -- -Chuck ___ freebsd-questions@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-questions To unsubscribe, send any mail to "[EMAIL PROTECTED]"
Re: RAID Performance Questions
Milo if you hunt around you should see papers/articles where it shows foe RAID 5 you need at least 5 drives before you any dramatic performance gains..(sun old Sun articles from around 1998 where they do the math as well). not sure about RAID 10, but again I *think* you need at least 3 drives in the stripe before you start hitting gains. To best test I'd put ALL the SATA drives into the RAID 5 or RAID 10 array and then see what happens. -- Martin On 1/25/07, Milo Hyson <[EMAIL PROTECTED]> wrote: I don't really have a whole lot of experience with RAID, so I was wondering if the performance figures I'm seeing are normal or if I just need to tweak things a bit. Based on what I've been reading, I would expect more significant improvements over a single drive. Here's my setup: * FreeBSD 5.4-RELEASE-p22 * AMD Athlon 2200+ * 512 MB RAM * 3ware 9500S-8 RAID controller * 8 x Maxtor 7Y250M0 drives (SATA150 - 250 GB each) * 1 x UDMA100 system drive I'm using a trimmed-down but otherwise stock kernel (see below). The array is configured as two units: a three-drive RAID 5 and a four- drive RAID 10. Both units have been fully initialized and verified. No errors or warnings are being issued by the controller -- everything is green. Using bonnie I get the following results with a 1.5 GB file: ---Sequential Output ---Sequential Input-- --Random-- -Per Char- --Block--- -Rewrite-- -Per Char- --Block--- --Seeks--- MachineMB K/sec %CPU K/sec %CPU K/sec %CPU K/sec %CPU K/sec % CPU /sec %CPU single 1536 42229 45.1 44379 19.4 17227 7.7 40819 41.6 44772 12.1 141.1 0.7 raid51536 21812 22.8 21876 8.7 12935 5.9 47283 48.3 61998 17.0 152.8 0.8 raid10 1536 21905 23.0 21999 8.6 14878 6.7 49036 50.1 64847 17.7 130.6 0.7 The write times of both RAID configurations are slower than the single drive (which is expected due to having to write to multiple drives). However, I wasn't expecting such a drastic reduction (about 50%). The read times, although faster, are only marginally so in per- char transfer. They're a bit better in block performance, but still not what I would expect. It would seem to me that a read spread across four drives should see more than a 45% performance increase. The highest rate recorded here is only a quarter of the PCI bus- speed, so I doubt that's a bottleneck. CPU load peaks at 50%, so I don't see that being a problem either. I also ran some performance tests with a stock build of PostgreSQL 8.0 to get a different angle on things. Two tests were run on each of the UDMA system drive, the RAID 5 unit, and the RAID 10 unit. The first tested sequential-scans through a 58,000+ record table. The second tested random index-scans of the same table. These were read- only tests -- no write tests were performed. The results are as follows: Unit Seq/secIndex/sec -- single 0.550 2048.983 raid5 0.533 2063.900 raid10 0.533 2093.283 Any performance benefit of RAID in these tests is almost nonexistent. Am I doing something wrong? Am I expecting too much? Any advice that can be offered in this area would be much appreciated. Here is my kernel config (the twa driver is loaded as a module): machine i386 cpu I686_CPU ident NAS-20070124 options SCHED_4BSD # 4BSD scheduler options INET# InterNETworking options FFS # Berkeley Fast Filesystem options SOFTUPDATES # Enable FFS soft updates support options UFS_ACL # Support for access control lists options UFS_DIRHASH # Improve performance on big directories options NFSCLIENT # Network Filesystem Client options NFSSERVER # Network Filesystem Server options CD9660 # ISO 9660 Filesystem options PROCFS # Process filesystem (requires PSEUDOFS) options PSEUDOFS# Pseudo-filesystem framework options COMPAT_43 # Compatible with BSD 4.3 [KEEP THIS!] options COMPAT_FREEBSD4 # Compatible with FreeBSD4 options SCSI_DELAY=15000# Delay (in ms) before probing SCSI options SYSVSHM # SYSV-style shared memory options SYSVMSG # SYSV-style message queues options SYSVSEM # SYSV-style semaphores options _KPOSIX_PRIORITY_SCHEDULING # POSIX P1003_1B real- time extensions options ADAPTIVE_GIANT # Giant mutex is adaptive. device apic# I/O APIC # Bus support. Do not remove isa, even if you have no isa slots device isa device pci # ATA and ATAPI devices device ata device atadisk # ATA disk drives device atapicd # ATAPI CDROM drives options ATA_S
